Okay, saturday I'm hauling a load of scrap down to the yard when my check gauges light comes on. I'm pegging the volt gauge. I downshift and pull over as quickly as possible. get it cooled down and shut it off. No hot batteries, no hot alternator, wire are cool enough to the touch. It is a balmy 3*F outside when this happened. I started it back up and it continues to happen thoughout the day. I noticed that if I watched the gauge and let out/went to neutral/idle right as it climbed, it would peg at 18 then stay for 4 seconds and then go back down. If I stayed in it, it would peg and stay, no matter how long I took it to an idle. the time I stayed in it longest I had to shut it down while rolling and restart to get it to go back to 14 volts. at idle, you can let it run as long as you want and it won't spike. driving around town with varying Rpm's it won't do it. it only does it on the highway at a constant RPM. this was all saturday, and now its monday and I need to be working with this thing. Its still cold here and I'm wondering if the temp has anything to do with it. I also swapped the right battery thursday night with a dead one. it started hard at first, but now is fine. I drove it 150 miles friday with it freezing cold and it didn't do it that night. just saturday morning. I have only driven it 15 miles around town without the trailer since then, and it hasn't happened again. I can't imagine the alt being bad as it is working "too well". Volt reg is in the PCM as I gather from reading about 20 threads on the subject. most of the complaints in the search were of people having low volts. almost no complaints of high volts.
options:

wait til it happens again/ burns something up

buy a new alt even though I might not need it

try to find a pcm for mine to swap in and check it

externally regulate it (I couldnt' find this tech article in the FAQ's even though I searched.)

If any of you guys have a suggestion I'm all ears
thanks,
Kelly

 

oops, subscribing

 

does anyone have the info on how to do an external regulator for my alt?

 

https://www.dieseltruckresource.com/...hlight=voltage
look for Infidel's post

Have you verified with a multitester to make sure it is in fact over charging, and not just a faulty gauge?

 

no I have not as I can't get it to do it unless I'm on the highway pulling. it did it the whole way there and back on SAT and now won't in town. havne't pulled since then, but I have the gauge in the truck in case it will do it for me. thank you for the reply and link

 

Hook your multimeter up to the cig lighter plug. cut up an old acessory cord and hook the mulitmeter to it. now you have a way of driving around and watching your voltage at the same time

 

AWESOME, thanks. that'll make it easier because when it came to an idle it would be back down to 14 (by the time I got stopped)

 

I don't know if they still have it, but Radio Shack used to sell a voltmeter that plugs into the cigarette lighter for under 20 bucks.