Who's the Alternator Expert?

[VRaptor SpeedWorks, LLC]

I have a GTM here that the alternator is not working. Has 3 pins in the alternator side of the connector but only 2 pins/wires at the harness connector. Doesn't appear that either of the wires in the connector have power to them with ignition on? Any clues? I'm pretty sure this is just a stock GMPP engine harness for LS7.


168732168733168734

[TheHelixx]

I think the red is the exciter pin from ignition. Check this out.

https://paceperformance.com/p-3980-serpentine-wiring-connections.html

[crash]

Those diagrams are not real straight forward...at least for me.

I have wired a few alternators and while some of them are "single wire" models, for the most part an alternator will require three to four wires.

1) Charge wire (B+) that goes direct to battery via large main fuse.
2) Exciter wire that goes to switched positive with fuse.
3) Load which is usually to switched positive or ground(depending on alternator setup) with fuse.
4) S wire that goes to Batt + with separate fuse.

EDIT: I did edit my original post based upon the wiring diagram I found online. I would normally not do this and leave what I had written and just post a correction, but I did not want incorrect info posted, so based on the diagram in my next post the above info is correct. That said, while it does jive with my previous experience, it is also based on someone elses diagram.

[crash]

Here is the best diagram that I found. The S is separate because it needs to be fused, and the Load does connect to switched positive as opposed to ground. Again, through a fuse.168760

[VRaptor SpeedWorks, LLC]

Looking at the diagrams that both of you posted, it would appear to me that the red wire in the B pin of the connector is the "Lamp" wire....which I would assume should have +12V on it when the ignition is on? My meter shows 0.15V on that wire with the ignition on.....so not sure if this is something like a pulse that is supposed to come from the ECU to get the alternator going in place of the light bulb or resistor in your diagram, Crash? Or maybe the alternator on here is just not compatible with this harness?

[VRaptor SpeedWorks, LLC]

Well, right or wrong, I got it working. Talked to a guy at Speartech (thinking that might be where the harness came from) that told me to cut the red wire (pin B) and run that wire to a 470 ohm resistor tied to Ign+. I ended up running that to the pink wire in the main coil pack connector for the LH bank. Fired the engine up and have 13.7V.....so hopefully that will be a permanent fix.

[TheHelixx]

The Subarus were notorious for this issue. If the bulb in the cluster burnt out it would open the 12v circuit back to the alternator and it wouldn’t charge. If you don’t have one at all then fooling it with a resistor would be like manipulating a bulb. Either way problem solved. :cool: