77 D100 does not start, various test done from the service manual result in a drop of voltage at the black box from 12.7 at the battery to 10.4 at pins 1,2 and 3. All other tests in this section pass. Trace the circuit and get less than 1v drop up to the red end of the resitor. Unplug the other end gets less that 1v drop, plug it in and I get 10.4 volts. Check the resistor and its good. Unplug the alt and regulator and I get less than 1 v drop at the resistor. Swap in a new regulator cause it is cheeper than the alt, no good.

Q Can I just replace the brush set (Standard CX15) or am I missing something? I looked at a cheep-rebuild-how-to and it was just bearings, brushes and clean up the contacts. I don't need bearings (now) I just need it to start again.

Does it even click when you try to start it?

Take a good, heavy gauge jumper cable and run it from the positive post on the battery to the big terminal on top of the starter. Then see if it starts. If it starts your problem is in the cable that runs from the battery to the starter. If it doesn't post back here.

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

Jeb, it cranks over fine and it sounded like it was just going to catch as I turned the key off. I heard somewhere that that is an indication of a bad coil. Swapped the coil and it started right up. Once. Then I replaced the diz cap, rotor, wires and plugs. plug 5 and 6 were way fouled with grit closing the gap, the rest looked great, a nice tan. The cap looked like the floor of a welding school. I thought that woul do it. No joy. I took the book, read through the diagnostics and preformed each, step by step. At the voltage reading at the ECU pins, I got 10.4 v at pins 1, 2, and 3 which indicates a fail if more than a 1 v drop. I traced through the circuit from the firewall block into the cab and back out into the engine bay. At the resistor, when the downstream connector was removed, I got less than 1 v drop, when I reconnected I got 10.4 v, or a failure. disconnected the voltage regulator, 10.4, disconnected the reg and alt and I'm back up to 11.8 v which is a pass. Buy a new NAPA reg, no joy.

Which brings us up to this post. I'm planning on changing out the brushes in the alt and see if that was where the drain was, but I don't want to keep chasing my tail either. I was planning on replacing/buying a spare for the other stuff, but I don't want to buy a NAPA alt. I plan on getting a cheap OEM one from the U-pull-it and rebuild it, but haven't and don't want to have to rush it. A brush set is $10-$15 at autozone.

What do you think?

What is your voltage at the battery with the engine running and the voltage at the alternator with the engine running?

This thread may help you: http://www.slantsix.org/forum/viewtopic ... +regulator

If you want to rebuild it this is place where I get my alternator parts from.

http://store.alternatorparts.com/chrysl ... parts.aspx

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82 D150-225/727
02 Dakota-3.9/5 speed
87 GMC C7000-8.2 Detroit Diesel/5+2

I'm confused. If the engines cranks over fine, but doesn't start, why are you working on the charging circuit.?

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Jeb - I'll take those readings next time I get it running, and thank you for the information.

Charrlie - I have a voltage drop at the ECU which, I think, is causing the no-run condition. In tracing the ignition circuit, I came up with no faults. Looking at the wiring diagram there are branches off this circuit after the resistor that include the alternator and regulator. When I unplugged the alt and reg it eliminated the voltage drop. My concern is that there is a partial short to ground in the alt. I've replaced the reg with new.

I think I'll unplug the reg and alt and see if it will start.

I also didn't check all of the branches off this circuit, I think the WWW motor and cabin fan and WW washer motor are branched in also. I can unplug those and isolate the circuit better.

It would be nice if I could unplug something and have a runner. At least I'd know what to fix.

Man, I'd like to take a run to the dump on saturday. My wife is loading up the bed with leaves and branches....

If there’s a short to ground in the alternator, it wouldn’t give you any response at all. In situations like this, the best way is to isolate the basic circuit and see if it works, then add the other loads one by one to see which one gives you a voltage drop. I hope you isolated the issue, please let us know what you found out.

pcb layout

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'65 4Dr Valiant

Like so many others, I fixed the problem and dropped the thread on this. I was looking for another topic and one of the newbies, like me, was complaining about this; fix the problem and then no follow-up on the conclusion.

To close this post, I bought a $30 GP test kit off ebay, plugged it in, ran the tests, identified a bad control module, had one to swap in, which I had done before to test if that was it (more on this later) and the truck sprang to life and has been running like a champ since.

What I did wrong: When I was swapping in good components to check if it fixed the problem, I was disconnecting the old unit, plugging in the new unit and GROUNDING WITH A TEST LEAD.

Many people have told me in the past that 90% of all electrical problems are the result of a bad ground. When I bought the truck I went around and and undid, sanded, lubed, and reassembled all the grounds with those star washers and yet when I was looking for the fix to this problem I chose to ground with an allegator clip on a test lead. Doh!

Live and learn if you can, and if you can't, just try to remember to do what the smart folks told you to do.