Found that diagram online somewhere. The 1998 FSM on mitsubishilinks seems to be missing the whole circuit diagram section at the end. But I compared this to the 96 FSM and it seems accurate, just drawn differently.

Last night I tested the 2 little wires that plug into the back of the alternator.

The yellow was fine - it's getting full, unswitched battery voltage at all times.

The switched white wire gets voltage when key is turned to ON, but it's 1 volt less than battery voltage. I tested at the connector and then further up the wire with same results.

With the dash bulb not working, it looks like white wire can only be getting power through the 'generator relay'. So I'll check that out. Is it possible for a relay to go partially bad and cause a voltage drop like this without breaking the connection entirely?