Charging Issue?, I'm terrible at solving electrical problems Options

[sdoolin]

Voltmeter shows between 10V - 12V at idle (and everywhere else). Voltmeter drops to 10V when headlights, flashers, and wipers switched on. Multimeter across the battery terminals at idle reads 12.5V.

Alternator was verified good several years back when I built this engine.

I'm not sure what to check next?

[sdoolin]

OK, so I checked some more things, and I am NOT GOOD with a multimeter. But, here's what I found (all measurements at idle):

Battery = 12.5V
Green Wire from alternator and chassis ground = 4.5V
Brown wire from alternator and chassis ground = 0.05V (essentially 0)
Red wire from alternator and chassis ground = 13.8V

[Spoke]

OK, so I checked some more things, and I am NOT GOOD with a multimeter. But, here's what I found (all measurements at idle):

Battery = 12.5V
Green Wire from alternator and chassis ground = 4.5V
Brown wire from alternator and chassis ground = 0.05V (essentially 0)
Red wire from alternator and chassis ground = 13.8V

Are these measurements from the 3 wires from the alternator connector at the relay board?

If the D+ red wire at the alternator connector on the relay board is 13.8V, then the alternator stator is functional.

If the large red wire from the alternator to the starter to the battery is in good shape but the battery is measuring 12.5V it would appear that the diodes in the alternator may not be functional.

If you charge the battery, what voltage do you measure while charging. If the battery can charge to 14V while charging, again the discrepancy between D+ and VBAT may be because of alternator diodes being damaged.