1991 D350 Cummins allison 6 speed. The temperature gauge needle is swinging wildly back and forth and the speedo Is acting goofy also. The battery seems to be about to explode. Replaced regulator again and alternator but problem persists? Any ideas?

We fixed it or the wife did, she suggested ground strap problems and sure enough the strap got left off during the allison swap.

 

'91 is a special year for Dodge Cummins trucks.
A '91.0 and a '91.5 have very different wiring and transmission stuff going on. Which one do you have?

Also are you sure you have an Allison transmission in that D-350. That would certainly not be a factory transmission option in any 1st gen Dodge.

 

Yes did a $17500 transmission swap.

 

So.....the problem is fixed with ground straps?

 

Is it over charging? ...Mark Sorry, didn't read the last line

 

It sounds like a $17,500 transmission swap does not come with ground straps, those are an extra charge item you need to ask for... And I thought the $800 South Bend Clutches I use on my builds where dropping some coin.

To the OP I am glad you got it figured out.
Props to the wife for providing the solution.

 

That's about what they cost new, sadly. I watch a 1979 Chevy c60 (gas) pull a 2020 chevy duramax all over the road.. transmission blew apart.

When a young kid fights an old man and says a diesel can always out pull a gas engine.. I own a c60 and man can that old iron pull/haul a load. I want to say that is what his costed with labor though, covered under warranty (It just happen!). New trucks (diesel) are just way out of reach these days, 40-70K deep

 

It didn’t fix all the problems. The ground straps solved the issues with the gauges, but the battery is still cooking. The picture should be familiar to most of you. Putting out 14.1. With the Chinese regulator. I switched to the third known bad regulator to get home. Is 14.1 volts overcharging? I plan to try to get a mpoar regulator tomorrow.

 

I would not be concerned at 14.1V. Depending on the load on the system and the condition on the battery it should be ok.

13.8V - 14.2V is what I would expect to see at any given time on a healthy charging system.

Those Chineseum flavored VRs are junk vs the Mopar units, but regardless of the flavor, running a ground from the back of the block to the VR mounting screw seems to buy them a little time.

 

Whats that big 2/0 wire for?

 

Have you put a meter on your battery to see what the voltage from the battery is? It is obviously overcharging. Mine turned out to be too much resistance in the green wire to the vr. The last 3 inches felt like a nail from over heating. The vr reads the voltage from the ignition switch. Run a wire directly from the battery. I recently destroyed 600 bucks worth of agm batteries with this problem...Mark

 

The starter is now on the other side. That is what the big 2/0 wire is for.

 

A problem which many have is there is a voltage drop between the ignition switch and the voltage regulator. This makes the VR think the voltage is to low and it boosts the field of the alternator to bring the voltage up. This is probably what is cooking your battery. This is what cooked my battery. I finally had to add a relay to the system to put the battery + directly to the VR. The original wire going to the VR from the ignition switch energizes the relay.

Edwin

 

I agree with Edwin and Mark. I added a ground wire from the back of the motor to the ground at the firewall at the VR mounting screw. Then I started to strip the 2 wires out of the loom to the VR to connect the battery + to the VR. That is when the lid to the bucket of oil I was standing on collapsed into the bucket. Used oil from the 12v92 Detroit’s in my boat. So, I had to stop for the day and call in a hazmat team(wife) to help clean it up. I will be back at it Saturday am. But I think you guys are right.