M1009 Generator 1 Circuit Problem

[Foxnut]

First post, thank you for all the learning while I've been lurking. I've had my M1009 for less than a year, and am enjoying having it from "my era" of service. I'm more of corporate guy than a car guy, but am trying.

My Gen 1 light is not coming on upon starting. Dash Voltmeter shows top of yellow. Gen 1 was rewound last fall and outputting as it should, but not reaching the front battery. Batteries both have around 12.5 volts. I pulled the instrument cluster last weekend and all the lights are working (on a bench with a 12 v source anyway, but that's another problem for another day).

I've pulled the plugs from both alternators, and done the key on / off thing. Red wires (1/2) have voltage (12.5 / 25 V) with the key off. Brown wire from Gen 2 has 25 V with key on.

The brown wire from Gen 1 is 0 volts with the key on.

I pulled the Gen 1 brown wire from the harness and found where it entered the firewall and scraped off some insulation there. The ohm meter from there, back to the plug is only 0.1 ohms.

The charging circuit wiring diagram shows the brown Gen 1 wire ending in a jumble of squares in the bottom middle of the page (I guess that symbol is the firewall?). Where do I go next? In the truck it looks like into the back of the fuse panel, but the diagram doesn't show a connection between the two. This is my first circuit tracing attempt and it seems to have given me the slip already.

Advise greatly appreciated!

Charles

 

[Keith_J]

Figure 9 of appendix F in the -20 shows that block with a mirror image next to it, that is the engine firewall connection. The brown wire circuit continues on to the instrument panel where it make connection with one side of the light bulb (idiot light) for that alternator. From there, the wire continues on to the fuse box where it is switched by ignition switch.

That same brown wire also serves as the "ground" for alternator 2. It is +12 volts so with the + terminal of the back battery (24 volts to ground), it is only +12 volts. The #2 alternator's +24 volt excite wire has a relay on it so it will also shut off with the ignition switch. So if the brown wire is not making +12 volts at the fuse box (blown fuse), both alternator lights should be illuminated with key on, engine off.

If I were a gambling man, I would look at the #1 alternator light socket as the source of your problems.

 

[Warthog]

Read the first few pages of the troubleshooting section of the TM 9-2320-289-20. It will help you understand how to read the wiring diagrams.

Never a good idea to remove wire insulation in the engine compartment. It will expose the copper to moisture and corrosion.

A trouble spot for the GEN1 circuit is the firewall plug itself. You need to remove the center bolt and pull the plug apart. The terminals are usually covered in a black goo and will effect the circuit. A can of electrical contact cleaner and an old toothbrush will do wonders.

That jumble of squares you see is actually the terminals of the firewall plug. Each square will show you which wire is which. Refer back to the explaination in the first few pages of the troubleshooting section.

 

[Foxnut]

Thank you, both. I will give a try as soon as I obey new orders from the Pentagon that may delay me till tomorrow... Charles

 

[Foxnut]

Okay, pulled the firewall plug apart and found things the expected black and nasty. Did several iterations of spraying contact cleaner and scrubbing with the tooth brush (I'd been to the dentist not to long ago and had a freebie). Shiny now, but Yuck!

Also cleaned the contacts again on the Gen 1 light socket.

In any case, still no Gen 1 light coming on at key turn (and no charging of front battery).

Next step on the brown wiring diagram looks to be a diode (now that I get the mirror image thing). I've no idea where it is, what it looks like, or with these symptoms if it's a factor.

What's the next logical step? Am I overlooking something in the trouble shooting guide?

 

[Warthog]

Does your heater work? The heater fuse controls the GEN1 alternator circuit

 

[Warthog]

I know you are new but this issue has been covered hundreds of time. I have helped with many of them.

By doing and an advanced search for GEN1 as the Keyword in body of the thread and Warthog as the User you will find many of them.

Here is one that I just found: It gives you all the details

http://www.steelsoldiers.com/showthread.php?111575-Alternator-1-no-light - Post #16

PS: there is no diode in the GEN1 circuit. Ther is one in the GEN2 circuit.

 

[Foxnut]

And you have helped with this one--back up and running. It was the heater fuse. Thank you. And thank you to many previous posts by others so I was able to find the heater fuse (the -20 diagram was pretty tough on that one). On to windshield wipers...

 

[Warthog]

Spend time reading all the stickies for the CUCVs. It covers many of the issues you will have with your truck.

What is the issues with your wipers? Slow - remove the noise supressors

 

[Foxnut]

Thanks--slowly making my way through the stickies. It's the only reason I got as far as I did before calling the life line.

Wipers were outright in-operative. Washers are still.

Wipers have come back with "jigging things around". I hate that, because now I don't know the original issue truly was but I'm certain it will probably come back. I've pulled apart the easy to get at plugs, but haven't ventured into the steering column yet. They are a touch..."anemic" compared to more modern wipers. The noise suppressors..like electrical noise... as in the three capacitors? I will do some reading and cry out if I get stuck.

Right now I would love to get washers up with the snow storm coming and all the road treatments.

 

[Warthog]

At the wiper motor there are a group of three capacitors. Unplug and remove.