I have a 1997 3500 360magnum cab and chassis. I am having a problem with high volts. At an idle it is between 14.7 and 15.1 and at driving rpm around 16. The battery with truck off is at 12.3- 13.1 I have replace pcm and alternator and battery. While plowing, battery dies about 2 hours in. Just realized the voltage gauge drops while at an idle in any gear(except neutral and park) with fan going on high down to 8.5-9. Not sure what is going on. Cleaned all grounds and added some. A little baffled. Any help would be appreciated. Thanks

 

Sounds like the regulator is bad.

 

My thoughts too, but I thought the regulator was in the PCM (which he said he replaced.)

There's a mod for using an external regulator here. It's for a first gen, but concept is the same. Could always try it to see if it corrects your issue.

 

If it turns out to be the regulator, this place sells a kit for installing an external regulator that also eliminates the CEL staying on.

 

Thank for the info. Is there anything else it may be since I have put in 2 new pcm in the last year. They came from Napa. Only paid for one, the other was warrantied.

 

Just digging through the wiring diagrams in the FSM, and there are a couple of fuses it could be... Have you checked them all? Could also be a short between the PCM and the alternator, and the alt is picking up voltage from somewhere that is telling it to charge at the wrong times...

I've also seen and heard of bad battery connections causing random charging issues. Make sure the posts and terminals are all free of any corrosion.

 

Terminals are clean, no corrosion. I'll check all fuses tomorrow and look at all wires. I appreciate all the info guys.

 

Pay careful attention to the big 140 amp fuse... I've had two of them fail on me over the years (different vehicles) that still passed visual inspection.

 

So I checked all fuses they are good. Replaced pos factory terminal and cleaned terminals. Could not follow wires from alt to pcm. Checked wires at starter ok. Wires at tranny(driver side just behind linkage) which I believe are for nss are cracked right at plug and have some corrosion. Could this be the culprit? If so where do I get the harness?
Once again thanks for the info so far

 

Is the harness repairable? Changing it would be a friggin' nightmare....

Check your connectors at the PCM as well, make sure they aren't dirty/corroded.