[Jim760]

sounds like a short maybe? are you sure the bulb holder is the correct type for the dual filament bulb? its not uncomon for people to have changed them and not used the proper one. do the spades in the base of the holder look ok? not bent or anything? check if when you press them in, is one moving and trying to toch the other? (assuming yours is the clasic 740 front with dual filament bulb) if it is, can you confirm if its the 21w filament thats actualy glowing, but dim, or is it the 5w thats glowing?

as chris said the fault can flip roudn the car, check the ground leads coming from your tail lights.. them wee bugers can cause allsorts of weird reactions!