I have a 1997 ram 2500 diesel. It started having voltage issues where it would bounce from 14-16 volts down to 8-10 and then back up again, it would do it repeatedly for awhile but only in gear, would not do it in neutral. I figured it must be an alternator issue so I went and bought a new alternator, didn't solve the problem. Then we checked the wires off of the batteries, alternator, grounds, everything is tight and clean. We then installed an external voltage regulator thinking this would solve the problem. it did solve 90% of the voltage irregularities, but it would still randomly bounce up and down, but not for very long and always stopped. Worked for about a month and then yesterday the truck was running fine, no voltage issues at all in the last week, shut the truck off for lunch, started it back up a few minutes later and my gen light came on and voltage wont rise above 12, usually sits between 10-12 causing the gen light to come on. Any suggestions to something I could be missing? Im about on my last nerve trying to figure this out

 

Have you load tested both of your batteries individually?

 

Also, how did you wire in your external regulator and not have a light on?

 

yes, both batteries when truck is running are at 12 volts. I ran my power wire from my gauge fuse, since those have power only when the key is turned on, and I spliced it into the top post on the plug in, and then connected both posts to the alternator, I even wet as far as to add an additional ground to the regulator from the battery just in case. Today I went and got a new regulator thinking possibly mine was shot, replaced it and now the truck will run, voltage doesn't rise above 12, and as soon as the truck is shut off and you try to restart it, there isn't enough power, just clicks. I have had the alternator checked by 3 different places, im going to take it off and have it rechecked again, it is only a month old. My gen light never stayed on permanently with this bypass it only came on when the voltage went below 12 for an extended period of time. im not sure if this is normal or not being that everyone else seems to say it will stay on all the time? at this point im completely lost, I have no more ideas, if this doesn't work with the alternator I will go buy new batteries, if that doesn't work im going to hope the truck starts on fire and burns in hell haha

 

Just because the batteries show 12v, that does not mean the capacity is there. Go to a parts store and have your batteries load tested. They have a machine that puts a load on the battery and measures their capacity. This is much more accurate than reading the voltage.

Make sure the batteries get tested individually. Don't let them hook up a tester without removing the battery cables first.

 

Yeah you've gotta disconnect the batteries and load test them. You can have 12 volts but only 3 amps - not going to cut it but it'll still show 12v on your dvom. Load testing will show you the actual health of the batteries. You have to disconnect them because you can't really tell if one is bad when testing together.

So you cut the wires from the PCM to the alternator?