Trying to figure out why my 87 Camaro will not charge the battery. Alternator tests good, battery is good. Heavy battery cables are new with good positive connections to the stud on the alternator and grounded to the block.
I have a constant 12 volt on the S terminal, and a switched 12 volts on terminal F that is running through the lamp on the dash. Lamp comes on with key on engine off, lamp goes out with engine running. But battery voltage measures 12.4- 12.8.

I double checked the wires going to the plug on the alternator and I have 3 wires going through a loom to the alternator plug. A red wire, a brown wire, and a black with white strip. The red and brown wire are connected to the plug, but the black w white is not. Not sure where this wire comes from, I cant seem to find it on any of the diagrams?

Any help would be appreciated, the alternator I am using is a cs130 I believe, it has the 4 pin connector.