I would say that if its too dim that it doesn't work

And a tail, turn, stop lite uses a bulb(or two bulbs) with 2 different candle power that creates the tail, turn, stop function which requires a feed to the tail portion that will be fired directly from the headlight switch and a stop/turn function that will be powered via turn signal/brake lite switches-----there will be 3 wires, of which one is a grd and if yours is just grounded thru the housing to the STEEL fender---a rubber gromment around the lite housing will prevent the ground and poor continuity between separate fenders(old cars) body and frames back to the battery will prevent proper electrical flow