QuestionHi Dick,
I am a little confused on this whole "positive ground" situation and it's getting deeper by the minute.
Background: A friend was temporarily storing this truck for someone and after driving it for a couple weeks the truck wouldn't crank. He replaced the battery with a new 6v battery from Napa #7204 and it drove for a couple more days until the truck wouldn't start again. I got involved to "help" and suggested the alt/gen was not charging properly.
I started out by getting a 6v charger and checking the terminals on the battery which appeared to be loose. My plan was to charge the battery and get it started to trouble shoot some more. So I put the charger on the battery as I typically would red to pos. and black to neg. and the charger would click on and off. I didn't think much of this because I have a few "micro processor" charger for 12v systems and the click on and off all the time. When I went back the next day the truck was still dead. Starter would just click. So I checked all the basic electrical stuff like start button, starter solenoid and starter for corrosion. Everything looked ok. Next, I put my volt meter on the battery, with cables attached, and it read less than 1 volt! Obviously not enough juice to do anything. So I figured the battery was bad. Upon removing the battery cables, and checking the voltage without the cables attached, it spiked up to 2.15 volts. So I think I'm on to something. My thought was that the cables were crossed on the battery (i.e. the chassis ground was connected to the pos. terminal) which would allow the charger to work. So I charged the battery over night, with the cables disconnected, and it took a full charge. So, I put a negative battery terminal cable on and attach it to the chassis and then connect the positive wire to the positive on the battery. I go to start the truck and it was cranking enough to build oil pressure but didn't fire. Not knowing the vehicle, I began to check fuel supply and there was none. After putting 4 gallons of fuel in it fired right away and ran great.
With it running, I checked the voltage at the battery and it read 6.45 volts with only a little fluctuation.
NOW, this is my concern. Just tonight I'm hearing about a positive ground system and I HAVE NO CLUE what this means or if the truck is going to blow up...
Will you please provide me some insight? Is it a positive ground from the factory and how would I know if it has been converted to negative ground? What should I do next?
Thank You.
John
AnswerStep one is to immediately disconnect the battery, if you haven't already done so, because this situation can and will lead to an underhood fire if the battery was in backwards long enough to damage the voltage regulator.
On to diagnosis (and a little history): You are going to have to read this very carefully - do it step by step, and read all the way through it before you start. This is complicated and confusing, I know, but I don't know how to make it easy!
Many if not most of the vehicles built prior to 1956 were wired positive ground (because it is a better system). This includes all Ford, Chysler Corp and most "independent" products. GM was a notable exception, their vehicles were negative ground, which has now become the industry standard.
This means that the truck was originally hooked up with the + terminal of the battery connected to the chassis/engine ground, and the - terminal of the battery connected to the starter and every other electrical device on the truck via the appropriate switch or relay. The vehicle can be made to run either way, as long as the wiring is set up right and the generator and regulator are also set up for it.
We need to do some detective work to find out which way the truck is now set up to run (someone may have converted it to negative ground, is what I am saying, and we have to determine that).
I advise taking a step by step approach as follows:
1. Put the battery cables on the original way (+ to chassis, - to electrical items) but as you connect the last end of the second cable (which one doesn't matter) with everything turned off in the truck, check to see whether or not there is a spark as you tap the cable end to the connection. If you see a spark, don't connect it yet (we'll come back to this).
2. If there is no spark, go ahead and connect the cables and turn on the headlights - then go look at the ammeter (if the truck has one) and note whether it is reading a charge or a discharge. Probably it doesn't have one, so we'll have to find out another way, but if it does have one, this is the easy way. OR, if it has a voltmeter, see if it is reading below zero, or about right (6.5 volts). If it has no guages, post a "follow up question" to me and we'll find another way to do this.
If the gauge reads correctly ("discharge" from the headlight drain, or upscale on the voltage scale), go to step 3.
If the gauges read backwards (showing a "charge" when the headlights are on, (engine stopped), or showing a voltage less than zero), reverse the battery connections and go back to step 1, but with the battery now hooked up for negative ground ( - to chassis, and + to the electrical system). Then go to step 3.
3. Next, start the engine and monitor the battery voltage with your portable meter as you rev the engine to fast idle. If the charging system is OK, you will see a rising voltage as the generator replenishes the battery after the start - it will keep rising until it gets to about 7.2 volts, if everything is undamaged and hooked up correctly. If the voltage stays steady, and doesn't climb up toward 7.2 volts, the charging system is not working. The truck can still be driven this way during daylight hours, but you will have to "top up" the battery after every trip until you get the charging system repaired. Do NOT leave the vehicle with the battery hooked up, because a common failure mode for a damaged voltage regulator is to drain the battery through the generator windings, which can and often has resulted in the vehicle being destroyed by a nasty underhood fire.
As for what might be wrong with the charging system, that is another very long discussion - but let's get the polarity issue straightend out first, then tackle that issue, OK? My fingers are getting sore!
OK< all the way back to step 1: If, when you tapped the battery cable on the last connection there WAS a spark, do not connect the battery cables yet. Make very sure there is nothing on inside the truck (lights, radio, heater, anything at all). If not, then, find the voltage regulator and remove the wires from it, and tape the ends so they cannot touch anything. Do the same with the generator wires. Now tap the battery connection again - if there is still a spark, there is still something drawing current - look further until you find it, disconnecting things if you have to until there is no spark when you connect the cables. Once you get to that point, hook up the cables and do the tests of step 2 again. If the battery cable makes a spark when you tap it on the connection ONLY when the generator and voltage regulator are hooked up, there is a problem in the charging system, whether it is charging or not. Probably it is going to have to go to a generator shop for service, if you can find one in your area. Don't hook up the charging system in this condition - it could easily lead to an underhood fire. You can drive it that way, as long as you don't use the headlights or drive very far without recharging the battery.
Post a follow up report to me on what you learn from the above tests, and we'll take it the next mile.
Good luck!
Dick
