Question-------------------------
Followup To
Question -
Is it possible to test electrical components for my kids motorcycles (1977 Honda Z50 and 1990 Yamaha pw50)using my multimeter. They are very hard to start initially and have a weak spark. After they are warmed up, they run fine.
Answer -
Hi Joedy,
Send me an email address as requested. I'll return repair and test info files.
Respectfully,
Mark Shively
AnswerThe &!@^%*#! Thing Won't Start
Oh boy is this irritating... It's definitely frustrating when you can't get your MC started. The first thing to do is a process of elimination:
In order for an engine to start and run, it needs 3 things:
1. Spark at the correct time
2. A proper fuel/air mixture and exhaust flow
3. Sufficient engine compression
Sounds easy, right?
Cylinder Compression Check: If you just acquired the scooter, you should first do a full inspection before you try to get it running. Please see this page on restoration. If this is the case, I'd do a compression check first because it's easy. First check the quantity and condition of the engine oil. Add oil as necessary. I wouldn't change it unless it's terribly dirty. The engine could be bad so you'd waste the oil change. Hook up or purchase a good battery. Leave out the spark plug and crank the scooter for ~5 seconds. This helps to circulate the oil. Let it set for ~15 seconds and do it again. It's not a good idea to continuously crank the starter because it can overheat and wear prematurely. Most scooters need a minimum of 100 psi in compression to run start and properly. Compression should be checked when the engine is warm, but that's kind of hard to do if the scooter is not running. So just hook up a compression gauge and open up the throttle all the way. Crank the scooter until the needle on the compression gauge stops moving. This should take no more than 5 seconds. Very roughly, 100-125 psi is good, 125-150 psi is very good, and 150+ psi is great. If you don't have this level of compression then you have bad valves and/or bad piston rings. If you want, you can add a teaspoon or so of oil to the engine through the spark plug hole. Then try the compression test again. If compression is higher, then it's likely you have bad rings. The oil will seal the rings and give you better compression. If compression is the same, then you have bad/misadjusted valves.
Got spark? There are a few ways to check for spark. The easiest way is to remove the spark plug and put it back in the spark plug cap. Then ground it to the engine - you should be able to lay it against a non-painted portion of the engine. Make sure there is good metal-to-metal contact. A darkened area may help to see the arc. You should see a definite spark at the tip of the spark plug. It's hard to see in direct sunlight. If the color of the spark is blue, that means it's a strong spark. A white color is less strong, and a yellow color is weak. Most MC starting systems are a bit weak (compared to cars). Even a yellow spark should start your scooter just fine. Next, the spark must occur at the right time. Just about all scooters made since around 1980 have electronic ignition. These systems rarely can be set. This is good news. After working on maybe 50 MC's, I've never seen one go out of time. Scooters with points are another matter. You'll have to follow the timing procedure in the manual to get the timing correct. In general, the spark occurs just before the piston reaches the top of its stroke. There is a slight delay between the spark plug fire and the fuel-air mixture ignition. That's why the spark occurs a little early. Most ignition systems have an advance unit build in, so that as the engine speeds up the time of the spark retards a little bit and helps the engine fire the mixture at the proper time.
Starting Fluid: Assuming sufficient compression, squirt in a bit of starting fluid and see if she'll fire. If so, great! That means that you have sufficient compression and the proper spark. You should get the scooter to run for a second or so on starting fluid. If so there's a good chance you can get it running. One caution here - don't run your engine for long periods on starting fluid because it's hard on the engine.
Fuel/Air Mixture: The last thing is the fuel/air mixture. You could be getting too much or too little of either. If the scooter has been sitting for a while, it's likely the gas has evaporated and left a bunch of sludgy deposits. Ask the seller when it last ran. If it's been more than ~3 months, you should clean out the fuel system and the carb. Disconnect the fuel line and drain the old gas. I've been able to burn old gas with no problem by using it in my truck. Add fresh fuel and make sure it flows smoothly through the petcock (on the bottom of the fuel tank). If the petcock is controlled by vacuum, you'll have to draw a vacuum on the vacuum line in order for fuel to flow. The vacuum line will be the smaller line on the petcock. Do you get a good, steady flow of gas? If so good, if not, you will have to remove the petcock and clean it. The gas flow should stop when you release the vacuum. Next, you'll have to remove the carburetor and clean it. There are a low of tiny fuel and air passageways in the carb that must be clean it order for your scooter to run right. Carefully take the carb apart. This can be relative easy (on a 50cc scooter) or quite difficult (a Riva 180-200 has limited carb access and 8 separate hoses running to the carb). The carb has tiny passages that get gummed up. The scooter just will not run correctly if the carb is not completely clean, so take your time. I use a gallon container of carb dip (you can get a gallon at your local auto supply store for ~$10). First remove all rubber and gaskets or they will be damaged. After a ~20 minute soaking I blow out the carb with compressed air. You have to get all the jets and the passageways clean. Be sure the jets are clear, especially the starter jet. Sometimes carb cleaner won't clear out these tiny jets. Use a guitar/piano wire, a strand of copper electrical wire, or a tiny drill bit pin vise. Be sure not to increase the size of the hole in the starter jet or you'll change the tuning. Carefully reassemble everything, checking for cracks in the rubber carb boots and the gaskets. Replace them if they are old and cracked. Be sure and remove all rubber and gasket material first or they could get ruined. Carb spray cleaner also works if you're diligent. If you have an electric choke, check it to make sure it works. Check the resistance between the wires - you should see around 10 ohms or less. Measure the length of the choke assembly. Remove the choke from the carb and plug the wires into a 12V source for 15 minutes. The choke body should be warm. Measure the length again - it should increase by around 1/8".
Next, consider whether your exhaust pipe is clogged. This is especially a problem with two stroke scooters. The unburned fuel/oil mixture builds up in the exhaust pipe along with carbon over time. If the exhaust pipe is clogged, your scooter will run terribly or not at all. It can be difficult to tell if the exhaust pipe is clogged. The easiest way to tell is to remove it and try to start the scooter. It will be a bit loud - two strokes will sound like a chain saw. If it runs, you know were the problem lies.
How Was The Old Gas? Did the gasoline smell old? If the scooter has been sitting over a year or so, the gasoline will turn into a varnish-like stuff. Then you'll have some serious cleaning to do. The gasoline will have evaporated for the most part, leaving a sludgy, molasses like substance in the gas tank, petcock, fuel lines, and the carb. All of these parts will have to be cleaned. This is especially a problem in the carburetor. Thoroughly flush out the gas tank and gas lines with new gas. I've had good luck using the old gas (in small quantities at a time) in my truck. If the gas tank is not too rusted or dirty, you might be able to get away with just flushing it out. Pour in some fresh gas. Remove the lines from the petcock to the carb. Place a suitable container under the fuel line and draw air on the vacuum line to the petcock (if so equipped) and see how well the gas flows. The flow has to be more than a trickle. It should be steady and fairly substantial. If you get this flow, then you're ok. Run at least a pint of gas through to help flush the system. If you don't get a flow then it's likely your petcock is clogged. You have to remove it to disassemble and clean it. Carefully reinstall it on the gas tank or you could get a gas leak. Reassemble everything and try to start the scooter. It will take several seconds of cranking to get the gas to work its way from the gas tank to the carb. Hopefully it will start now! :>)
The Big Test: Install a new spark plug, especially if the engine is a two stoke. Clean or replace the air filter as necessary. The carb, air cleaner, and exhaust pipe are all carefully tuned to work together. Most scooters absolutely WILL NOT run correctly if any of this stuff is changed in a haphazard manner!
Double check all connections, then crank for 10-15 seconds. Did it start? Do you hear any popping, like the engine is trying to run? Most scooters will not start if you apply throttle while cranking. Honda scooters tend to start easier if you apply throttle just as the engine catches. Most Yamaha scooters will not accept any throttle at all until they warm up a bit. If the scooter catches, but doesn't start, let it rest ~15 seconds before trying again.
BASIC ELECTRICAL TROUBLESHOOTING
Electrical problems can pop up at any time and can seem hard to fix but they really aren't most of the time, anyway. Most everything can be "Proved" (tested) with an Ohmmeter and some things can be proved with a simple circuit tester.
You can get a good cheap ohmmeter, sometimes called a multimeter, from a hardware store or an auto parts store. They generally run about $20.00. If you want, you can pay hundreds of dollars for one, but for the tests we will be performing, a cheap one will work just fine.
An ohmmeter sends a very low power electrical charge through a wire and measures how much resistance there is in the wire to the charge going through it. This resistance is measured in Ohms. Your shop manual will give you the correct resistance for each wire that you test. The multimeter will measure a bunch of different things such as ohms, DC volts, AC volts, etc. Here are a few of the basic tests. They are all performed at room temperature (70 degrees or so). The word Continuity means voltage is passing through the wire from one end to the other. No Continuity means the wire is broken and voltage is NOT passing through it. Also, if we say something is wired in parallel, it means they are wired side by side. If two 12 volt batteries are wired parallel, the negative terminals would be wired together, and likewise for the positive terminals. This would still give us a 12 volt battery, only bigger. If something is wired in series, it means they are wired one after the other in a line (Christmas tree lights)(one bulb blows, all go out.) The two 12 volt batteries would be wired positive to negative, giving us one 24 volt battery.
A shop manual will be very handy to give you the Specifications on the different coils and wires. It also will have a wiring diagram that will give you the different colors of the wires you are going to want to test. Most of the specifications I give here are just general ones to get you in the ball park. The Shop Manual will give you the exact ones.
Before you do any testing, make sure you have a fully charged battery. Just because it will start and run without the battery does not mean it will run right. Time after time guys will bring a bike in and say "It runs good, and then it doesn't. It misses on one side then the miss changes to the other side." Some of them just will not believe it's a bad battery or the wrong size battery. "But it runs. It can't be the battery." But it can be the battery. If it needs a battery, and you take the battery out of the system, things can overcharge, overheat and burn out. If the system calls for a battery, make sure a good one, fully charged, is in there. The only time this would not be true, is when the ignition system is a magneto type and the battery is only used to run the horn and tail light. When I say "The right size of battery" I mean the battery must have enough amps to run all the things you want to test. If you don't have the right battery, you can use a big, fully charged battery from a car, but it must have the right voltage (6 or 12) and you must use big, thick, jumper cables. Do not connect the jumpers to the old dead battery. Take the old, dead, battery completely out of the bike. Connect the positive jumper cable to the positive cable on the bike. Connect the negative cable to a good frame ground on the bike. Now you can run your electrical tests. The fact that the battery is a lot bigger then the stock bike battery will not hurt anything. The electrical components on the bike will only draw the power they need from the battery. The battery will not damage the components as long as it is of the correct voltage. If you leave the dead battery in the system, it will try to pull power from the bigger battery. At best this will throw your electrical tests off. At worst the battery can explode.
Ignition coils:
Measure the resistance between the primary (12vdc small wire) wire and ground or ground terminal. It should be very low. Like .5 to 1.5 Ohms. The primary wire is the small wire going to the CDI box or points. Next measure the secondary (spark plug wire) wire and ground. (Note that on most bikes, the metal bar that passes through the coil and mounts to the frame is the ground for the coil windings) This should be quite high, like 6,000 to 13,000 ohms. If the coil is outside the specs given in the shop manual, the coil might be bad. Sometimes, a coil will work when cool, but fail when warm. When cooled, they work again. They make special test devices that test coils under load. They are nice to have, but are expensive. Remember to take the plug cap off before the test. The cap can add 300-5,000 ohms resistance, or more.
Sometimes the ignition coil can be located under the flywheel and be self contained. That is, the ignition coil and ignition stator coil are one in the same. These are usually found on mopeds and small European bikes.
Charging Stator Coils:
These are the coils that are under or around the flywheel. Sometimes they are both. The flywheel has magnets on it and these magnets produce a charge in the coils as the run around them. Usually there will be three wires, all of the same color, coming out of these coils. You want continuity (continuous connection) between the three wires with a low ohm reading like .5 to 3-4 ohms. There should be NO continuity between these wires and the ground. If there is only one charging wire coming out of the flywheel coils it is usually grounded and has a reading of .5-1.5 ohms between the output wire and ground. If there is no resistance the coil may have wires shorted together. If there is infinite resistance a wire is broken. Check the shop manual specs.
Some charging systems are alternators, and some are generators. There are also variations of alternators and generators. Note: some replacement coil sets have very short leads. You have to cut the old leads and plugs off the bad coils and splice them into the new system.
Ignition Source Coils:
These are coils, under or around the flywheel, that supply energy for the ignition. Usually, almost always, these coils are grounded. Usually, 300-500 ohms from output wire to ground. Often, but NOT always, if you stick a Circuit Tester on the charge wire and clip the other end of the tester to ground, then kick the engine over, you will light the tester bulb briefly. This indicates you are getting some kind of juice out of the coil.
Pick-up or Pulse Coils:
These coils tell the electronic ignition black box when to fire the ignition coil. Usually two wires, 1 to 3 ohms resistance between the two wires and no continuity between them and the ground.
Rectifier:
When a coil produces electricity, it sends current in positive and negative waves. The battery can only charge on the positive side of these waves. A rectifier has silicon diodes that only allow half the wave to get through. Between 1960 and 1980, many small engines had single wave rectifiers. Nowadays, most bikes have full wave, bridged rectifiers that have four diodes. All this rectifies or changes AC current to DC current to charge the battery. To test the rectifier, hook up the ohmmeter leads to one of the wires and to the ground (mounting) stud. Note the reading. Now reverse the leads from the ohmmeter and note the reading again. The exact reading is not all that important, but there should be a big difference between the two if the diode is working right. Test each of the wires this way. If any wire is very close in the two readings then the diode is leaking and no good. If there is no continuity, then the diode is shorted out and no good. Be careful not to turn the bolt holding all the diodes together. This can short them out. It is possible to test the rectifier with a circuit tester by adding a D flashlight battery in line with the circuit tester. You want to see the light illuminate in one direction, and not in the other. If a you blow the main fuse, it's possible one of the rectifier's diodes has failed and is letting current from the battery flow back to ground.
Voltage Regulator:
All current from the charge coils would over charge the battery if not regulated. A voltage regulator is used to keep the battery charged at about 12 volts. Your ohmmeter should have a DC volt scale. Set it at 20 volts and connect the positive and negative leads to the battery terminals. Make sure the battery is fully charged, so we get a correct reading. Start the bike and rev the engine. The volts should go up to 13.8-14.5 volts and then stay there. Much higher, and it will over charge the battery. Much lower, and the battery will never charge. Some voltage regulators can be adjusted to get the right charging rate. Modern regulators are not adjustable, and have a combined regulator/rectifier unit.
Capacitors:
On some older bikes (Mostly British, like Triumph, BSA, Norton, etc.) There will be a capacitor that holds or stores electricity for the ignition. They have a limited storage life of about 12-18 months if not in use. To test a capacitor, connect a 12 volt battery to it for about five seconds. Make sure polarity is correct (positive to positive, negative to negative) or it will be damaged. Let the capacitor rest at least five minutes, then connect a DC voltmeter (ohmmeter set to DC volts) to the terminals. When testing, wait a few minutes for meter readings to stabilize. A good capacitor should read at least 9 volts.
Zener Diodes:
They do the same thing as a voltage regulator. Without a good battery in the system, it tended to melt one specific wire that charged the battery. They need a good heat sink to help prevent this from happening. The best thing to do with these things is to throw them away and buy a real voltage regulator, but if you want to test them, here is the way.
1. Disconnect the cable going to the Zener diode and connect, in series, a ammeter, with the ammeter positive lead connected to the diode terminal
2. Connect a DC voltmeter between the Zener diode and the heat sink. The red or positive lead of the voltmeter must be connected to the heat sink, which is then connected to the frame. Remember, British bikes have positive ground, at least the ones with Zener diodes.
3. With lights off and battery fully charged. Start the engine while watching both meters and slowly rev the engine.
4. The ammeter should read zero until the voltmeter reaches 12.75 volts.
5. Increase engine speed until the ammeter reads 2.0 amps. The voltmeter should read 13.5-15.3 volts.
6. If the ammeter reads anything before the volts are 12.75 or if the voltage is higher than 15.3 at 2 amps, replace the Zener diode.
Rotors:
Some charging systems have rotors (armatures) that turn inside a magnetic field producing current. These usually have two slip rings separated by insulators. The slip rings can be on the nose of the rotor or on the side. There should be continuity between the slip rings, but not to the rotor body (ground). On some older bikes these double as an electric starter. These have a commutator on the end of its shaft. These are similar to a starter's armature. If they are worn you can cut and polish them a bit. They are tested like the slip rings: Continuity between every other commutator band, and no continuity to ground.
Brushes:
If the system has carbon brushes, they must move freely in their holders and be long enough to always be in contact with the slip rings. If you can't get a brush for an old bike, you can sometimes take another larger brush, and cut it down to the right size.
Flywheel Magnets:
These are usually trouble free. Back in the 1930s, 40s, and 50s, the quality of magnets were not so good. To this day, if you drop them or if they suffer a blunt strike, they could loose their magnetism. This renders them useless. A special machine is required to re-magnetize them.
Remember, the ohmmeter may have some internal resistance of about .5 ohm. Zero the ohm meter or hold the ohmmeter leads together to find out what that resistance is and subtract it from your test readings.
Sometimes the ignition, lights, turn signals, etc… will just stop working. Here is where the little circuit tester light can really help. You will need the wiring diagram for your bike so you can pinpoint which color wires are used on the suspected part that doesn't work. Check all the grounds first because they can get rusted and will not conduct electricity. Then check and see if you are getting battery voltage at the suspected part. If so, maybe the part is dead. If not, go back to the battery and check again for battery voltage. If so, work your way along the wiring until you don't get voltage. Check the electrical plugs (multi-connectors). Sometimes just plugging and unplugging them can cure things. If there are no plugs to check, you can still check the wire by piercing the wire insulation. Most circuit testers have needle like points for doing this. The hole tends to close up and heal it's self, you don't have to tape it or anything when you are done. If it's a switch, you can sometimes clean any corrosion with some electrical contact cleaner or with a pencil eraser. Look for places wires could be rubbing against the frame or touching a hot part like an exhaust pipe. You may have to remove the seat or tank to access wiring, or remove the headlamp shell. Be patent. It can take a long time to find the problem.
If you replace burned out bulbs with bulbs that have a different wattage than stock, it may cause problems. It can make the turn signals blink faster or slower. If it's a charging indicator light bulb it can upset your charging rate. It may not hurt anything, and then again?
• A lot of bikes now have safety, ignition, cut outs to keep you from starting the bike when it is in gear or to keep you from riding off with your side stand down. They seem to be putting them everywhere. If your bike will not start they must be checked. Here are some of the places I have found them.
1. Clutch lever: It must be pulled in, to start the bike.
2. Side stand: It must be up, or the engine will die when put in gear.
3. When the bike is in gear: The bike must be in neutral to be started.
4. Reverse gear: The rear brake must be applied to shift into reverse on most four wheel ATVs.
When you check for spark, the spark must jump at least 1/4" (.250") or more outside the engine. Just laying the spark plug in the plug cap, on the cylinder head, and getting a spark across a .030" gap is no good. It takes a lot more power to jump a gap under compression inside the engine compared to laying a plug against the head and watching for spark. Also, with some electronic ignition systems, you must spin the engine to at least 300 to 400 RPM. Any less and the anti kick back circuitry in the CDI black box kills the spark.
Voltage Drop Testing:
When measuring the voltage on a battery by putting the positive ohmmeter lead on the positive terminal and the negative lead on the negative terminal, you are actually measuring the voltage between the two terminals. The positive terminal reads 12.6 or so volts and the negative terminal reads zero. The wiring circuitry in the ohmmeter subtracts the negative lead voltage from the positive lead voltage (12.6v-0v=12.6v) and you end up with the reading 12.6 volts. What does all this mean? Well, if you connect the positive ohmmeter lead to where the power starts: the positive battery terminal and the negative lead to where you want the power to go, like a starter. Run the starter and you should get an ohmmeter reading of zero. If you get a reading, that is the voltage drop. This indicates resistance in the starter cable or in the connection to the battery or starter. Another way of thinking on this is that the voltage drop is the number of volts that you lost over that connection. The reading you get on the ohmmeter is number of volts you have lost. You can test the ground connection side of the starter, too. Connect the negative ohmmeter lead to the negative battery terminal and the positive ohmmeter lead to the starter body. Again, crank the starter. A DC circuit should use all available voltage, so the reading should read close to zero, or not more than .4 volts.
Don't forget to check the obvious; kill button off, switches off, etc…
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Electrical Testing
(Basic electrical troubleshooting tools)
Few things can be as frustrating as trying to troubleshoot an electrical problem on a modern street or dual sport bike, with their plethora of unidentifiable electrical components, hard-to-remove electrical connectors, sealed wiring harnesses, etc. Much of the trouble associated with fixing electrical problems can be attributed to a lack of proper tools and technique.
Your best friend when troubleshooting bike electrical systems is an electrical multimeter, sometimes referred to as a VOM (Volt-Ohm Meter) or just plain old multimeter. A multimeter reads current (amps), potential (volts), and resistance (ohms), each over a variety of ranges that the electrical troubleshooter must choose. Cheaper model multimeters can be had at Radio Shack for less than $20--more expensive digital models can cost hundreds of dollars. Nonetheless, no garage should be without one.
If you're buying your first multimeter, a cheaper model is recommended for two reasons. First, the measurements you'll need to make when working on your dirt bike are mostly crude kind of checks which require little real accuracy. Secondly, as a electrical neophyte, the possibility always exists to smoke the meter through a wrong connection or test procedure. While superior meters are better protected by fuses, circuit breakers and the like, the ramifications of frying a $20 multimeter are not all that serious. Bottom line: buy the cheapest meter you can find that offers some sort of fuse protection. And buy extra fuses too! An up-to-date electrical schematic of your project is also nice to have, especially when trying to identify various mystery components. However, it is not essential, and in a pinch can often be overcome by a little patience and common sense.
There are essentially three troubleshooting techniques, facilitated by the use of your trusty multimeter. They are: measuring continuity, measuring potential and measuring current. Continuity means that there is a electrical connection between two points, whether they be via a dedicated wire or through the engine or frame. Measuring continuity is especially useful for locating grounds, intended or unintended, checking switch operation, mapping out wiring harnesses (when a schematic is unavailable), checking fuses or connectors for good electrical contact, and so on. Continuity is checked by using the meter to measure resistance, selecting the R X1 scale and connecting the two leads of the multimeter, in parallel, between the two points for which continuity is in question. The R X1 range is used to limit meter pegging (which could potentially damage the meter), and is certainly sufficiently accurate for this simple test.
The meter essentially sends a low voltage signal between the two points (generated by the meter battery) and indicates whether the circuit is completed or open. Open circuits (no continuity) are read as infinite resistance (no meter needle movement), whereas a completed or closed circuit reads as zero (or near zero) resistance (full sweep of the needle). Caution must be taken when using your multimeter in the resistance mode not to run an outside current through the ohmmeter (i.e. checking for continuity between a hot battery terminal and ground), as this will either blow a protective fuse (on meters so equipped) or fry the meter outright. A good precaution is to disconnect the positive battery lead and allow sufficient time for any system capacitors to discharge (on machines so equipped).
Switch your meter to the voltage measuring mode when you need to find hot leads for connecting accessories, check the health of your battery or lighting coil output, and determine if power is reaching a malfunctioning component. A zero voltage check across two points will also tell you it's safe to do a continuity check without fear of meter damage. Voltage measurements are taken with the meter linked in parallel with the suspected potential. Most multimeters have ranges from a couple of volts to a couple of hundred volts, measuring both AC and DC. Surprisingly, you may need both capabilities as the output (lighting) coils of most bikes produce AC. While nearly all street and dual sport bikes rectify this AC voltage to DC (because it's easier on electrical accessories), enduro or trail bikes often run the AC right to the headlight and tail light.
If you're checking an ignition coil output or an unrectified lighting coil output, start by using the AC scale closest to, but not less than 12 volts. For rectified lighting/accessory voltage checks, again choose the scale closest to, but not less than 12 volts, from the DC choices. If the meter reads DC voltage backwards, simply reverse the polarity of the meter leads. With analog meters, it can sometimes be a little tricky determining what the actual voltage reading is, as there are usually several scales printed on the front of the meter. The trick is to look for the higher number of the range you've selected (i.e., look for a 50 if you've chosen the 0-50 VAC range) at the extreme right of the meter and that's the scale that should be used.
Current flow is measured using the ammeter function of your meter. The presence of current flow indicates that your lighting coil or battery is actually accomplishing some work. This is good if a head lamp, turn signal or the like is in operation, but bad if everything is turned off (dead battery syndrome). The ammeter function of your multimeter is useful for locating shorts or determining the draw of a particular accessory. Current measuring requires a slightly different technique, as the meter has to be in line (in series) with the circuit. Most multimeters are capable of measuring a couple of amps draw, way on down to milli- (1/1,000) and even micro- (1/1,000,000) amperes. When using the current measuring function, choose a high current range and work your way down to lower ranges. This prevents the dreaded meter pegging and associated damage.
Trouble shooting techniques are dependent upon the notion that current flow should be zero with the ignition and all accessories turned off. If you're still reading current at this stage, then you've probably got a problem with a shorted or failed accessory. Start disconnecting things until the current draw goes away, and that'll isolate your problem. Beware, however, of charged capacitors discharging and reading as current flow.
