It is fairly easy to trace the circuit out on the board on the taillight assembly and to see what bulb holder should be where as you can tell what part of the holder should be touching the ground circuit and then you can identify the brake circut and the running light circuit and first see if you have the wrong bulb holder in the right place or even the wrong bulb in. Try to use all euro style bulbs with oval nubs on the bottom of them instead of the US style round nubs. If your circuit board is messed up, which mine was on a brand new assembly, the running light copper ciruit can be touching the brake light circuit on the bulb holder too. I had to cut one of my brake circuits and then jumped the brake light with an alligator clip or something like that. I try not too look at it and it has been working great for over a year now.