My lightbar was doing the same thing. Turns out the left lamps' hot wire was grounding out on the inside of the housing and that happened in spite of me having wrapped that connection with electrical tape. So drop each lens and look for a spot on one of the wires (or at the connector) that is charcoal in color. Fix it and work the wires were they won’t rub on anything.
Could be worse, you could be blowing the lamp itself!
