Here is the schematic. Looks like the oil light and the gen light both come off the key switch.
Looks like it could be coming through the starter, starter solenoid, generator, regulator, push button starter switch, or key switch?
Is it possible it is coming back through the light switch through the right hand lights?
I think I can isolate and test the starter, switch and solenoid by pulling the wire off the key switch at the "ST" terminal and that would test out that circuit.
If I pull off the "BAT B" terminal from the key switch, that would isolate the key switch from the left battery.
If I pull off the "A1-GEN" wire from the regulator, and both the oil and Gen lights go out, that would isolate the generator, but if the oil light stays on, then the Generator should not be the problem.
I may want to pull off wire "LT B" from the key switch to isolate the lighting circuit on the "B" side if nothing else tests out as above.
If anyone sees any "holes" in my logic, let me know.