
To my annoyance, the bulbs would work fine in running light mode, but the turn signals did not work. When I reversed the bulb in the socket, the turn signals would work, but the running lights would not.
Thinking I had a couple bad bulbs, I called superbrightleds, and they told me the pin layout. I tested it - and it was correct. So what was going on?
I got my meter out and measured the voltages at the bulb socket. With one lead on the ground terminal in the socket I measured +12V at the running light terminal - and -12V at the turn signal terminal!! WTF?? No wonder the LED wasn't working!
After scrutinizing the schematic, I realized that I had an aftermarket harness in there that flashes the side fairing light when the turn signals are engaged. Looking at the harness, I realized it worked by reversing the ground and turn signal leads, so that the running light actually runs through both the running light filament AND the turn signal filament - and that the fairing light uses the turn signal filament for its ground.
I removed the harness, and the LED worked perfectly.
I'm going to rework the harness and put a small relay in there so that I can keep my flashing fairing light functionality while running LED lights.