M1078 Alternator Problem

I went to play with my M1078 today and noticed I was getting a low voltage reading on the gauge. All the battery connections, alternator connections, regulator connections, and battery volts are good. I haven't done all the trouble shooting in the Niehoff guide, but did check the regulator readings with the engine running and got no juice on the "E" side. I'll do the actual alternator check tomorrow, but I'm guessing I'm gonna have to buy a not so cheap part here.

So, I did some quick eBay shopping just to get an idea on price. All I really see are the 400 amp generators. Electrically, they should work, but I'm wondering if they will even fit and operate properly without modification.

Thoughts, feedback, ideas?

If you have a 12v/24v 200amp niehoff, I am in need of the brush guard if you replace it and have a junk core. The one I have on the regulator has 2 indicator lights for the 12v and 24v sides to indicate they are charging?

I am not able to help with your questions as I do not have any experience with your series.

Sorry to hijack your thread.

I have the mtv dual volt alternators new but they state A1 variant use.

Hmm. I wonder what the difference is? You got a part # I can research? How much are you looking to get for one?

I'll verify the AMPS and let you know.

I can look Monday. I have complete upgrade kits.

Alternator is charging. Regulator failed at the "E" connection. The trouble shooting guide says to repair "E" circuit. I assume that means replace the regulator since everything else on the circuit is after it and there is no juice at the regulator. I anticipated this and new one should be here today. Should I be looking at something on the "E" circuit as the cause for the regulator failure?

Thanks.

Wait. If I jumped from the alternator to the "E" connection and everything came to life, including the regulator lights, wouldn't this suggest a problem between the alternator and regulator rather than the regulator itself. By repairing the "E" circuit, are they saying there is an issue in the alternator to regulator harness? I think I'm over analyzing and confusing myself.

did you fix it ?

Just fixed a couple hours ago and a heads up to all MTV owners! The problem had nothing to do with the alternator or regulator. There are two wire harnesses that come up from under the cab and enter the dash compartment right next to the throttle control linkage. If the wire loom doesn't come up high enough, the linkage can rub the wires and eventually wear through causing a short. One of the wires in that bundle is the hot wire to the energize side of the voltage regulator. In my case, that wire was damaged and fried. Therefore, no juice to the regulator and the resulting charging issue. Every MTV owner should remove the dash panel and check this area. Yours might be fine, but I seriously doubt mine is the only one. I also consider myself lucky. That wire is the 28V side and the short area was pretty charred with a couple other wires needing repair. It could have easily been a disaster. This was not an issue that the truck had when I got it. The chaffing may have begun, but the voltage was fine.

A few simple precautions / upgrades can prevent a mountain of headaches in the future. I will post this info elsewhere for those not following this thread.

Be well.

that's awesome , good thing to insulate before a problem like this occurs. I have a spare 12v/24v 200amp niehoff. I thought about keeping it but I may sell it.

Here are the pictures for what caused my voltage problem. The engine harness comes up through the driver's side floorboard / foot well and enters the dash compartment just behind the throttle pedal linkage.

As the pedal / linkage moved up and down, it started rubbing the wires.

Eventually, it ate through and shorted a wire. In this case the wire was the "Energize" wire supplying the voltage regulator.
The short burned through two other wires as well.

Sure wish more members would do threads like this one, a GOOD searchable title, a problem, a CAUSE, AND a FIX

Repaired wires and everything came back to life. Make sure the loom comes up high enough and zip tie / secure the harness away from the moving linkage.


I would suggest everyone check this area on their trucks. I doubt mine is the only one with this potential headache. As the old saying goes, "An once of prevention is worth a pound of cure."

I did the same thing and used some zip ties on the harness in mine. I was in there to grease the throttle linkage to see if it would move easier and noticed how the wiring harness was really close.

I just got one in from GovPlanet that was in great shape, but the pics showed the cover off the fuse panel and the cover etc. pulled off everything below the fuse panel. This vehicle also does not charge, so I'm wondering if it's the same issue? Hmm. Something to look for before I get carried away with my multimeter. Thanks for the tip. Looks like it may be a known problem with the A0 trucks which explains why someone pulled the lower panel off. Interesting.

So, just sorted my problem out. Jumpering the 'E' terminal on the alternator to +24V made it all work, which meant no exciter feed to the alternator. I looked for the wiring problem detailed above, but everything was cool on my A0 truck, so out came the manual. And yeah. So, some dimwit had mixed up the relay for the Exciter with the relay meant for the Starter. Both are 24V. Both will plug right on in. But the Starter relay is a 4-pin, and the Exciter relay (K11) needs to be a 5-pin. Swapped them back and...voila! All works as it should. I have to thank the horrible, horrible 'flow-chart' style -20 manual for pointing me there ('horrible' in that I hate the flow-chart-mechanix-4-dummiez approach which takes 120 pages to convey 12 pages worth of info.)

Hope that helps others.

I came across this one day. I don't know if will help anyone in the future.