Charging Issues

[rmesgt]

Hello everyone. I have been trying to diagnose the charging problems on my M1009. I have read the thread about how to check the alternators while they are on the truck, but I don't understand the directions. My alternators don't have the markings discussed in the thread. The charging system hasn’t worked since I purchased this vehicle. I have been all over this truck fixing this and that, but I haven’t yet figured out the how to repair the charging system. Here are some things I believe to be true:

My “Gen 1” dash light never lights up when the key is in the on/run position. I have verified that the light bulb, socket, and ribbon cable on the back of the instrument cluster are FMC.
My “Gen 2” dash light never shuts off when I start the truck or I am driving.
The dash volt meter never goes to green when I am driving.
I can usually start my truck 8 to 10 times before the front battery fails, causing me to charge the front battery.

Here are my assumptions. Please let me know if ANY of my assumptions are false or incorrect:
The LEFT (drivers side – DS) alternator charges the front battery (closest to the grill).
The RIGHT (passenger side – PS) alternator charges the rear battery (closest to the fire wall).
The RIGHT (PS) alternator MUST BE an isolated ground alternator.
The LEFT alternator MAY BE an isolated ground alternator.

I cannot be certain the alternators on my M1009 are factory alternators. I have attached a pic of the stamped information on the body of each alternator. Please let me know if these are “factory” alternators. Can someone please tell me how do I identify an isolated ground alternator?

 

[Skinny]

There is a fiber washer on the ground stud isolating it from the case. This is an easy way to ID it, I'm sure it also has infinite resistance between the casing and the ground stud. That's a guess but it shouldn't be connected electrically in anyway.

I'd rebuild both units, dope the wiring out to make sure it doesn't have any shorts or opens, and replace both the charge bulbs with non-LED units. Too much wonky stuff happening here.

 

[rmesgt]

OK.... I am a dumb ______ (Insert your own adjective). Charging problem solved by adding a grounding wire from the engine to the isolated ground post on the drivers side alternator. Charging just fine now...

 

[MarcusOReallyus]

NO, not dumb. The isolated ground concept is a new one to most people. Takes a while to get your head around it.


But.... You have a problem. If you have grounded the isolated ground alt via its ground post to the engine block, it's not isolated ground anymore and there should be some smoking wires going on. That should NOT work unless the truck has been converted to 12v.

That ground post should actually be connected to the + side of the front battery. Yeah, that's exactly what I said. A "ground" connection straight to a hot connection. Like two D cell batteries in a flashlight.


Can you post some pictures of your battery wiring? And maybe take some voltage measurements? I'd be interested to see what voltage you have from the rear battery hot post (+) to a the ground (-) post of the front battery.

 

[doghead]

NO, not dumb. The isolated ground concept is a new one to most people. Takes a while to get your head around it.


But.... You have a problem. If you have grounded the isolated ground alt via its ground post to the engine block, it's not isolated ground anymore and there should be some smoking wires going on. That should NOT work unless the truck has been converted to 12v.

That ground post should actually be connected to the + side of the front battery. Yeah, that's exactly what I said. A "ground" connection straight to a hot connection. Like two D cell batteries in a flashlight.


Can you post some pictures of your battery wiring? And maybe take some voltage measurements? I'd be interested to see what voltage you have from the rear battery hot post (+) to a the ground (-) post of the front battery.

I think you may be confused. The drivers side alternator does require a ground wire.

 

[Tow4]

NO, not dumb. The isolated ground concept is a new one to most people. Takes a while to get your head around it.


But.... You have a problem. If you have grounded the isolated ground alt via its ground post to the engine block, it's not isolated ground anymore and there should be some smoking wires going on. That should NOT work unless the truck has been converted to 12v.

That ground post should actually be connected to the + side of the front battery. Yeah, that's exactly what I said. A "ground" connection straight to a hot connection. Like two D cell batteries in a flashlight.


Can you post some pictures of your battery wiring? And maybe take some voltage measurements? I'd be interested to see what voltage you have from the rear battery hot post (+) to a the ground (-) post of the front battery.

He's talking about the driver's side alternator. That ground can be to the engine block since you can run a non-isolated ground alternator on the driver's side. I do wonder where the factory ground wire went though.

 

[rmesgt]

I will try to get some photos on Tuesday. I have a wiring diagram that I used to trace out my charging problem. That is how I determined that I was missing the ground wire. I haven't seen any smoke coming from engine wiring. As for what happened to the original ground wire, I have no idea. This truck had several non military owners before I got it. I have been trying to undo many of the "fixes" that didn't quite work out

 

[rmesgt]

My M1009 is still up on jacks so I cannot yet get the photo's, but I thought I would attach a copy of the reworked wiring diagram I used to fix my truck...

 

[MarcusOReallyus]

I think you may be confused. The drivers side alternator does require a ground wire.

"May be", nuthin'! I certainly am!

He's talking about the driver's side alternator. That ground can be to the engine block since you can run a non-isolated ground alternator on the driver's side. I do wonder where the factory ground wire went though.

Yeah, makes you wonder what else got hacked.....