Okay, Then we are back-feeding from the alternator.
The indicator light may have something to do with it.
Your alternator has a plug or three separate wires?
Can't remember.
Can you get to the indicator bulb?
If so, remove the bulb from the socket and try again.
If it stops, the problem is on the ingnition switch side of the lamp, if not, on the alternator side.
Anything could have happened, you may need to un-loom the harness, starting at the alternator, look for a PO splice or melt.
Dave