Ok, I suspect I know the answer from hanging around here but I am going to ask anyway, because I hope the truck gods will be nice to me. It is nasty cold winter up here in southern Alberta again and shortly after I loaded my truck with groceries today I heard a strange chime sound. The red light on the dash let me know that is the 'Check Gauges' alarm. I scanned the gauges and the voltage gauge was sitting on the bottom peg I pulled off the road and shut down the truck. After almost a minute, I restarted the engine and voltage read between 14.4v and 14.7v. On the rest of the trip home there was a brief period (less than 60 seconds) where the headlights dimmed and I saw the voltage drop to 12.3 volts, then the lights lit up and all was back to normal.
Is the charge / voltage regulator in the ECM on these trucks or is it external or in the alternator?

 

I believe the voltage regulator is in the PCM. There are some write ups on how to adapt in an external voltage regulator. If not on this forum, do a search on cumminsforum or mopar1973man.

 

suspect brushes first. as greg stated the regulator is in the pcm. there is a ground wire from the battery to the cab on the drivers side, check it next. if it turns out to be the regulator the external one is for a ford so you will just have to live with the humiliation. it is carquest VR438 pm me for a drawing if you need it and I will make one and send it to you.

 

Thanks for the fast responses guys. Today everything seems back to normal except it is charging just a hair higher than yesterday. I actually suspect that for today, my digital voltage gauge is too sensitive for my own good. Last night on the way home it was running between 14.3V and 14.6V. This morning during the drive (at -23C in case that matters) it was running between 14.5V and 14.8V.

I can't afford to be stranded so, assuming I make it through the next few days, I will put a new alternator on over Xmas vacation.

 

mine does that too every once in a while, but with mine it's just the grid heaters

 

I replaced the alternator today. From reading the FSM that should have been a 20 minute job. It took me almost 2 hours. The nut and bolt on the bottom of the alternator is a really special treat to get at. I think the steel lines in my way were for the transmission heat exchanger. Does anyone have any special tricks for the bottom nut and bolt? Oh yeah, the spring tensioner has a really good load of tension on it!!!