Bill is correct, I had the same thing happen with the front running lights. had the wires switched so I was using the turn part of the bulbs filament which is brighter for my running lights. When I went to hook up my tail lights. I tested them first at my battery to see which one was the brake/turn wire (brighter)and which was the running light wire (dimmer) then marked them with a piece of masking tape I also installed a new ground off the light housing mounting bracket to the frame near the tail lights.