1992 W250, factory auto; that I put a Getrag in (and left the auto PCM.)

I’ve been reading every charging issues post on here that I can find. This one got me going on the right track as he was also not getting the proper 8v to the CPS, but his PCM fried before he got to the bottom of the issue. So...

I have 12v at pins #3 & 9, ground at 11 & 12 like I should. I have continuity from the CPS to the PCM on the supply and signal wires, and no resistance. Also from both field terminals on the alternator to the PCM. I have ~1v on the supply wire to the CPS. ASD relay checks out good (so did the spare I tried just in case.)

When the check engine light first came on I was 10hrs from home. It charged intermittently for almost half the drive home. When it seemed to quit charging, I did the external VR conversion in a parking lot. That overcharged at 15.5v for an hour or so, and then started charging intermittently as well before finally failing a couple hours later. Once home, the alternator tested at ~11v output.

I then installed a good used alternator, and a 60s era mechanical VR. That charged at 13v intermittently for a day or two, before giving out. Alternator then tested at ~10v output.

I obtained a supposedly good used PCM, and installed it with a new(rebuilt) alternator. Zero charging. That’s when all the above tests were done. I have the kit to convert the alternator to internally regulated, but with the external regulators not working out for me I’m thinking it probably won’t help either.

I’ve been trying to follow the diagnostics procedures manual, but don’t have the electrical specific one (yet.) I’m running out of ideas in my limited electrical knowledge. Any direction would be greatly appreciated!

 

I have suggested this a couple times and it has turned out to be the case....is you grid heater stuck on? Remove one of the two small wires to each of the solenoids on the drivers inner fender and see what happens.

 

I remember seeing you post this before, so I’ve checked that too. They operate properly (including not operating when battery voltage is too low.)

In looking into the internal voltage regulator kit install, I realized I’m not getting 12v to a field terminal on the alternator. I’ve checked both field wires though, to the ASD relay and ...shoot I am blanking on where the other goes. Both have continuity, zero resistance, etc.

 

Is the air gap set properly on the CPS? And you have good clean grounds? I'm just suggesting the easiest first...

 

Run a separate 4 GA wire from negative bat post to engine block. Run separate wire from block to frame and body.

Pretty sure Jim Lane suggested to have ground wire from alt to neg. battery. Extra grounds are cheap, and protect against loss of connection.

Side note: buddy has a 2007 1500 hemi quad cab. Ground straps under truck broke. Fried his pcm.