QuestionQUESTION: Hi Howard,
Not sure why I couldn't do a follow up to the last reply you sent so I guess I'll just do a new thread to bring you up to date.
I did most of the tests you suggested. The only one I wasn't able to do the 12v light test on the large brown power wire at the alternator post due to inaccesabilty. Everything else I was able to do and this is my data.
I did the voltage drop test of the cable system which read 0.1v well below the max of .5v and also a drop test of the power wire to the alternator which came in at .07v, well below the max of .5v.
I then did several versions of battery/alternator tests:
Engine Off / No Accessories: 12.56v
Engine Off / With Accessories On: 11.99v
Engine On / No Accessories: 13.57v
Engine On / No Accessories but Revving: 13.57v
Engine On / With Accessories On: 13.20v
Engine On / With Accessories On and Revving: 13.23v
So these are just below the preferred range of 13.8v to 14.5v you mentioned.
This is strange because it would appear that the alternator is putting out some charge even thought the parts place test said it was putting out none at all. And if it is working to a degree then why would the ignition/battery light still be staying on when the engine is off?
I think we are finally getting to the bottom of the this. Just a bit of tweaking and I should be good to go.
My guess is that the ignition/battery light should have been connected to the small post all along. When I did the test you suggested by unplugging it the light was off as it should be. When I grounded it then it came on as it should. When I removed it from ground it went off as should. Then the mystery comes back. I then plugged it back into the spade and it stayed off and didn't come back on like it should. It only came on after the key was turned off.
So I did a little experiment and left it unplugged and taped it off so it didn't touch anything and I went back through my tests and they were pretty much the same. So I'm not sure it's needed at the moment but I still feel that the diodes got zapped somehow thus making the light stay on.
So I'm going to replace the alternator and hook it up right this time and I should be good to go.
In the meantime how do the readings I have seem to you? Do you think I'm getting sufficient charge to use the car for a few days until I have the time to put in the new alternator? And do you think my experiment with unplugging the exciter wire is okay and won't do any harm? Don't worry, I'll NEVER unplug a cable again with the battery running no matter what a "mechanic" tell me.
I just can't understand how the car and alternator lasted so long for the previous owner if the exciter wire were hooked up incorrectly. At least I'll have it right this time thanks to your help!
Thanks again for everything!
I'll write and epilogue when all is done.
Rick
ANSWER: The exciter wire (Brown w/black tracer) is not powered with the key in the off position so it can be grounded and nothing happens. When you turn the ignition key to "ON" you power up the exciter wire. If it were disconnected from the alt, the light would not come on. The only reason the light comes on is because the alt exciter post is a ground. But as soon as you turn the key from "ON" to "Start" and the engine starts up and the alt starts to charge (because the exciter wire has excited the field in the alt and it starts charging). When it starts charging the exciter post becomes (+) and a Positive on both sides of a bulb makes the idiot light go out.
Now, if you have a idiot light "ON" with the key off or out of the ignition switch you should remove the exciter wire from the alt to see if it goes out. If it does then the exciter post must be (+) which means the diodes or the regulator has failed and it is powering the exciter post when that post must be a ground. The reason it can light the light with the key off or out of the switch is because there are other items connected to the ignition switch that act as grounds when the key is off or out of the ignition switch.
As for your question of will the car be ok for a while with such a low out put. The ignition and the ECU and fuel pump do not draw a lot of current so you could probably drive a long way but if the charge light stays on with the ignition switch turned off, that will run the battery down so you could not leave it off long. Also you did not run a very important test and that is the test light between the (+) brown wire on the large post. This tells you if there is a large battery drain with everything off. It can run a battery down over night or even in a few hours. It is the same as leaving a light on all the time.
Howard
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QUESTION: Howard,
Let me make sure I have everything clear here and please indulge me because I am just a novice without a lot of experience and you are indeed the expert or you wouldn't have been giving such great advice to folks here at allexperts.com.
I understand the principles of how and when the idiot light should be on. I believe I agree with you that the diodes are probably bad in this latest alternator which is feeding back and keeping the idiot light lit.
As I see in my experiment with this exciter wire, that the idiot light indeed went off when unplugged with the ignition switch on. It then went on when grounded and off again when removed from ground. It did not go on when reconnected with the ignition still on even though it should have as you said. It only went on when the ignition was turned off which it shouldn't do. Thus I can see the conclusion regarding the diodes.
So I guess I'm just trying to clarify that I'm ok for the moment having it disconnected since it doesn't seem to be affecting my already somewhat low alternator output, since those numbers are staying about the same whether it's connected or not. Would the diodes also be contributing to the lower alternator output? Since I'm getting some output then I'm guessing that if I'm not running accessories then it should be sufficient to keep me going until I do the replacement in a couple of days when I have a few hours free.
Now bear with me if I'm repeating myself or repeating something you have already ssid.
Once I do the replacement, I should leave the new alternator set up as it is out of the box with the capacitor that came with it hooked into the spade terminal, connect the large brown wire to the large post as before, and then connect the exciter wire to the small post via the spade adapter they have on this configuration? That would seem to be correct since touching the exciter wire to the small post on the current installation made the idiot light come on as it should.
For what it's worth I couldn't do the important test of the test light between the brown wire and the post because it was physically impossible to get to it and disconnect it. I could only do that by removing the alternator. If I'm at that point then I would already be putting in the new alternator. Should I do this test on the new alternator once I'm at that point to rule out any other issues before finishing the job? I wouldn't think there would be any issues because I haven't been having problems with discharge and battery drain. The only drain that would have been happening was the idiot light staying on and I've been taking care of that by leaving the negative post disconnected. Last night I left the negative battery post connected since I had the idiot light disconnected so the light couldn't drain the battery. The car started right up this morning with no hesitation and this time the idiot light came on briefly at start up and went off a couple of seconds later as it should when all is functioning properly I guess if the battery was draining overnight then there shouldn't be a drain somewhere being caused by the connection that I should have checked as you suggested if possible.
So I hope I've summed everything up in a somewhat coherent manner. I'm sure it must be difficult for you to ascertain what someone means when they are trying to put in laymans terms what you know in a more technical way.
Thanks so much Howerd for taking a look at this and giving me the answer for a proper hookup once and for all.
Rick
ANSWER: Rick, I think you are on the right track. Here is a method to test the diode pack when you get the old alt off and even test the new one before you put it on.
Lay the alt on the head and connect a jumper wire from the case of the alt to either the negative post of the battery or the engine itself so it is well grounded.
Then take a 12v test light and connect the clip to the (+) post of the battery and touch the large post of the alt. The test light should NOT light up. If it does there is a bad diode in the diode pack that changes the AC current that all alternators and generators produce into DC voltage that can charge a battery etc. The test light should not even burn dimly.
In your case where the charge light is on with the key off and once you disconnect it and reconnect it and the light goes out you may have only a regulator problem because I never seen a diode fail and get good again when disconnected again.
The main diode pack has at least 4 diodes in a box pattern and sometimes some can leak and they will cause the test light to light dimly and I have put them on a scope and you can see a wave pattern of a small amount of AC current being put into the system. This causes a lot of problems and can drive a computer crazy too.
You can't test a regulator if a alternator is bad. The only test I have for the regulator is the final result of it's out put. And only if it has a good alternator.
I would do the voltage drop test of the negative system after you install the alternator by connecting the positive test lead to the engine itself and the negative test lead on the battery post (not cable end) and hit the starter and watch a low voltage reading.
If I were at Jaguar when they designed the Series III car I would have told them to put that (GM air pump that is only used for a few seconds when starting) down under and put the alternator that is used all the time up top. Everyone throws the air pump in the trash anyway when it locks up.
Howard
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QUESTION: Ready to shoot the car or myself. Just spent about 6 hours under the car wrestling things off and and getting them on again. I used a friends lift to make it more easy but it still was a tough job. Bottom line is the new alternator is in and ZERO output. Same voltage reading with engine running as when off. Put in brand new battery to make sure whole system would be new. Only positive side is idiot lights are ok. Comes on at ignition and goes off right away. Does not stay on when car is off.
I can't imagine 3 reman alternators in a row would be bad so the problem has to be in the car and it's either killing alternators or just preventing them from putting out voltage.
I hooked everything up as directed but not sure if pulley is right because I'm getting a strange sound. Belt is tight and pully spins belt but something is making racket and of course no voltage output.
Anothe bit of info that I don't think would affect anything other than maybe giving an incorrect reading is that the fellow whose lift I used put his test meter on the battery posts to check output and he put the test leads in backward. Pos lead to neg battery terminal and vice versa. Could this have caused a problem? This is the same guy who said removing the negative cable was the was to test for a bad alternator. Of course I now know that's incorrect thanks to you.
I'm out of money and patience. There has to be a simple answer to this somewhere. Feel free to write to me off post of you don't want to clog up this site with my dilemma. My personal email is
Thanks Howard.
Rick
AnswerThe fact that the light is on with the key on, clearly shows that the alt is a ground at the time and the fact that the light goes out when you start up clearly shows that the charge light post has become positive which means it has started charging.
Connecting a test meter up backwards can not harm the car or alternator. It will not even harm a meter. Most just either will not read anything or it will show a negative reading.
You must have skipped one of my tests. You either don't have a good connection from the large post on the alternator to the battery or you have a bad ground strap from the engine to the frame to the battery or bad connections at the battery posts.
It is unlikely you have had three bad alternators in a row from a parts house. Or your volt meter is faulty.
Did you change the pulleys or did it come with a pulley on it?
Howard
