Well, there's three contacts, two on the bottom of the bulb, one for ech set of LEDs, and the outer case. The outer case connects to the socket which connects to the light frame, through the fender to ground. According to how I read the wiring schematic, each contact at the bottom of the bulb is energized by the power on, and by the brake switch sending +ve to the bulb bottom and grounding through the bulb case, so I don't understand how polarity could be backwards. I'll give it a run and see if maybe it's not hitting a voltage threshold before illuminating. Otherwise I'm going to have to send +ve to the light frame, insulate it from everything else and switch the ground via the brake light and a dedicated wire for one set of leds, which sounds like a whole lot of work.