The license plate lamps on my 67 MGB are shorting. There is only one wire to each fixture (the hot wire) and no ground wires were provided. From what I have been able to ascertain, the grounding is through the bumper to the chassis. Well, this gounding is apparently not very effective. Would running a small wire from the bulb holder to the lens screws help? I have tried taking the entire assembly apart but it didn't help.