1988 245, original Bosch alternator. When car is off and key is out, battery light stays lit. Battery light is not on when car is running, so I assume it is charging correctly.

Read another thread on here suggesting that if the light goes out when the small red wire is disconnected from the alternator, then the short is in the alternator rather than in the wiring harness. The light went out when I yanked that wire this AM, so I bought a new regulator/brush assembly at the dealer and installed it this afternoon. No change. I've never had an alternator issue that wasn't solved by a new voltage regulator assy, so I'm pretty lost here.

I have a few questions:
-inside the alternator, are all the electrical parts contained within the regulator/brush assembly? There isn't a separate diode or rectifier lurking elsewhere in the alternator?
-should I just open up the harness containing the heavy red wire, the small red wire, and the oil pressure sender wire and hope I can visually locate the short? Could I confirm the presence of a short in that stretch using an ohmmeter between the two red wires before opening up the harness covering?
-anything else I should be checking as a possible cause?

thanks,
John