Alternator Wires

[Cletus09]

My m1009 has been having problems with the passenger side alternator (gen2). I had it tested and it was found to be "bad" by autozone. So I ordered a rebuild kit from cucvelectric.com and now I await its arrivial. my question is about the wires hooked up to the back of the alternator.

I compared the wires behind my gen2 to another cucv, I found a difference that I questioned was the cause of the gen2 failure. Under my hood, the top post had a solid red wire on it. The bottom post had a small red wire and a red with white stripe wire, and the resistor on it. The small threadless post in between had nothing on it, not even a cap.

Under the hood of the other cucv: the top post had the small red wire and the solid red larger red wire. The bottom post had just the wire with the white strip on it and the resistor wire on it. The small post in between had just a cap.

I know the gen1 circuit is much different, but it does have a small black wire on the posts in between the top and the bottom post. what does the middle post do?

I would like to know if the small solid red wire belongs on the top post or the bottom post before I hook everything back up. Also the Gen2 light is not working, I didn't know if that had anything to do with it or not. I previously was not getting the rear battery to charge, and it went bad after only two years of use. That why I had gen2 tested and why I am going to rebuild it..

 

[Keith_J]

The middle post is the tach signal for the Standard Test Equipment for Internal Combustion Engines port, that big round connector with screw cap on the bottom of the dash.

There shouldn't be another wire connected to the negative post. Did the twin plastic connector have two wires on it? Should be one 2mm red and a 2mm brown. The red is the voltage sense, goes to the 2 terminal of the recessed connector. The brown is the idiot light and remote switch, it tells the regulator to energize the field when the ignition is switched on.

If there is no voltage to the sense line, there will be problems.

I just installed both alternators in a 1009 yesterday so this is fresh on my mind. And I even bench tested them without having to wait in line at Auto Zone. I bought a replacement 2-connector pigtail at NAPA, then used a small 12 volt battery and some wire. Held the alternator in the vise, then spun the pulley with a wire wheel in an angle grinder. The pulleys were rusty so it did two things at one time.

Some may call me a hack but I get it done.

 

[Warthog]

First off the GEN lights must be working for the alternators to work. May be a missing bulb, bad bulb or a dirty connection.

Second are you sure the small red wire isn't orange? Looking at the wiring diagram E-11 or F-11, you will see a small orange wire hooked to the top post (positive) of the GEN2. It is only used for the STE-ICE diagnostic port.

When the trucks came from the factory there was a cap on the STE-ICE tach port. Most have been lost over the years.

 

[Cletus09]

Thanks you both so much! I will be getting a new excitor plug or "pigtail" with the rebuild kit and make sure that I am getting power out of both of them. I checked the GEN bulb once before, but I found nothing wrong, the bulb was good and the connection wasn't perfect but not terrible either. Is there anything IN the alternator (that may be replacing) that could have gone bad and caused the GEN light to not come on? An yes, I think the smaller wire is orange, sorry 'bout that.

 

[Keith_J]

Ok, orange makes sense.

Yes, it is possible for the regulator to fail to where it won't turn the light on when running. It also won't turn on when the ignition is on and engine not running.