I recently got a “Check Gauges” light and quickly discovered that the battery isn’t charging. At first I thought it would be a simple fix — just replace the alternator. Unfortunately, it hasn’t been that straightforward. I installed another alternator (although it was a used one), and the system still isn’t charging. I suppose it’s possible the replacement alternator could also be bad, but that seems very unlikely. I even opened both alternators up and checked the brushes and other components-everything else looked fine. I double checked, and its installed correctly and the two wires are hooked up.


I’d think this is something I should be able to handle — after all, I built the entire motor myself and have replaced plenty of more complex **** than this. Still, I’ll admit I’m a little embarrassed to even ask, but I think I may need some help diagnosing an issue with my alternator… yes, a ******* ALTERNATOR!!!

Below is the wiring diagram for the charging system reference. I guess the next step is to do continuity checks on the exciter wire. Has anyone seen this before? What am I missing here?
Thanks.

 

OP: "Has anyone seen this before? What am I missing here?"

Yes. I have seen this before.
Take ( both) alternators to the local auto electric rebuilder shop, and have him BENCH TEST them.
Then, have him SHOW you which wire excites the alternator, and confirm that the excite current draw is in spec ( around 70 Milliamps or less should light it off.

 

Yeah, I was going to suggest the same thing. I'd make sure to thoroughly check the exciter wire as well. Mine was hanging on by a thread and needed to be repaired.

 

Were these current production AC Delco alternators?