Ok guys here we go. 

My truck is a 2000 2500 w/ 24v cummins and here is my problem. I bought the truck back in September 15 and has run like a top up until now. I am driving to work this morning and my voltage dropped out and dash light can on saying "check gauges". My immediate thought was ok I just lost the alternator no big deal. Pulled it off and went to Napa, had it tested before I bought a new one and surprisingly it tested OK. Bought a new one anyway for good measure and had it tested before I walked out of the store, also had both my batteries load tested while I was there and they check out. 

Get back to work and throw the new alternator on, drive it for maybe 10 minutes and same thing as before. Volta drop out and I get the check gauges light. Ok I'm stumped. Do a little research and find out that it could possibly be the plug at the back of the alt because it looked a little sketchy to me or it could have been that the voltage regulator in the PCM took a dump. Look up the price of a new PCM vs doing a voltage regulator swap and decided to go back to Napa and pick one up and run it like the old days. 

I followed Moparmans instructions to a tee and it seemed to work. Drove maybe and hour and a half and I'm watching my volts going up and down continuously until it spikes and I get another check gauges like only this time it's over charging. 

I have checked all my grounds that I can find, I have check continuity between batteries and resistance etc. My question is before I spend 500 on a new PCM that my problem is the voltage regulator in the PCM. All my gauges work on the dash so it can't be the crank position sensor ( I think). Please if anyone has any other ideas or input please send its way. I have done everything that I am capable of doing to fix the problem short of replacing the PCM.

Thanks guys 

had this exact issue when my ground cables on the battery were trashed.  

 

How are your cables and ends looking?

14 minutes ago, Me78569 said:

had this exact issue when my ground cables on the battery were trashed.  

 

How are your cables and ends looking?

They a good not great. And I went over literally every ground I could find. I guess it couldn't hurt to put some new betterybcables and terminals on and see. 

have you jumped out of the truck with a multimeter and read voltage on the battery posts when the dash flips out?

I have, but not when I have had an over charge warning. Something like 14.37 at both batteries. 

carry a multimeter with you and jump out and measure next time you get the spike.

The alternator grounds thru the mounting bracket. My truck had some resistance on that ground because of the paint on the bracket so make sure a good ground there and make sure of the heavy ground cables bolted to the block are good also.

Not sure of much help here but, good to check anyhow.

BTW, check the PCM ground going to the firewall and factory ground connector on the passenger battery.

1 hour ago, Me78569 said:

carry a multimeter with you and jump out and measure next time you get the spike.

Have one in the truck going to take it out tomorrow until it happenes again and report back. 

Try doing a voltage drop test. No more than .2v on the positive cables and .3v on the negative cables. Just today I had a car with a dead battery and low output (13.0v). I did the voltage drop test and had .1v drop on the positive cable and .5v drop on the negative.  I found the grounding wire for the alternator loose at the intake manifold.  I tightened the bolt and alternator output went to 14.2v.  

 If you are unfamiliar with this type of test these videos will help.   

https://www.youtube.com/watch?v=UhT2cNCfTXc

 

4 minutes ago, IBMobile said:

Try doing a voltage drop test. No more than .2v on the positive cables and .3v on the negative cables. Just today I had a car with a dead battery and low output (13.0v). I did the voltage drop test and had .1v drop on the positive cable and .5v drop on the negative.  I found the grounding wire for the alternator loose at the intake manifold.  I tightened the bolt and alternator output went to 14.2v.  

 If you are unfamiliar with this type of test these videos will help.   

https://www.youtube.com/watch?v=UhT2cNCfTXc

 

Here is the article on it as well.