M1008 CUCV Passenger side alternator issues

[goldneagle]

I bought a M1008 truck from GSA. It was a former fire company truck. Had signs of blown battery on passenger side. Juanprado helped me with the passenger side alternator. After messing around with it for a while he noticed someone had reversed the 2 large red cables on the alternator. (that probably explains why the battery blew up) The alternator was toast. Fuseable link was damaged at the 24volt bus bar. I repaired the wiring and installed a new isolated ground alternator on the passenger side. I also replaced the alternator on the driver side since it was not charging the battery either.

Now the alternator on the driver side charges the front battery. The passenger side alternator was not charging. After testing I determined that there was no negative current going through the red with white stripe wire. I used the wiring diagram to locate the other end of the wire. At the 12 volt terminal the fuseable link had melted inside the blue insulation. I replaced the fuseable link and tried again. Still not charging the back battery. I tested the red and white strip wire and got ground. So I know the two main cables are hooked up and passing current as they should.

Now I am thinking maybe its the red and black wires that go into the plastic connector. I know the red 1 goes tot the 24volt bus bar. Not sure where the other wire goes. What is the function of those 2 thin wires and where does the 2nd one go?

 

[Barrman]

I tried to follow along, but got lost with the different red wires. Could you take a picture of what you have in the truck now?

 

[goldneagle]

It's all the original wires. No modifications. I need to know where the 2 thin wires (exciter wires) go to from the passenger side alternator.......

 

[richingalveston]

I believe they go to the diagnostic port.
I know the drivers side goes there for the tach buffer. not sure on the passenger side. I thought it only existed on drivers side.

 

[Barrman]

The exciter wires go to the relays under the dash.

The diagnostic wire goes to the STC/ICE port as Rich said.

 

[cpf240]

No diag wire ( tach output ) on GEN 2, passenger alt. The exciter wires should go to the GEN 2 relay under the dash, and the GEN 2 light in the instrument cluster... I believe...

 

[goldneagle]

Now that i know where the relays are located I will replace them tomorrow. Hopefully that will resolve the problem!

 

[goldneagle]

OK i replaced the relays today and still no charging on Gen 2. Neither the gen 1 or gen 2 lights come on at all. From what I see in the wiring diagram there is supposed to be a diode in the circuit. I do not know what it looks like or where it is located. Can any help me work through this charging problem?

 

[LastFbody]

You probably already know this one, but I'll mention it anyway. The alternator (at least true of gen 2) will do absolutely nothing if the dummy lights aren't working. Found that one out the hard way complete with the visit of a tow truck..

 

[dependable]

Check the CUCV stickys, I believe Warthog has posted some good diagrams of all the relays and diodes. I know there is a diode in the wire harness located near the back of the air cleaner.

Also, here is a alternator service manual that has not been posted here for a while. The stock alternator in these is the 27 SI