defective dimmer switch [new or not!] .... crossed wires on one of the head lights [one high, one low on at the same time] .... plug assembly along the way with some stray bit in it that shorts between the indicator wire and something else, like park light wire .... using a meter you may be able to track where voltage to the indicator is coming from when on low beams, check any accessible point back to where the wire ties into the high beam wire at the dimmer switch
Bill
