should be....black is ground, brown is taillight and the yellow and green wires are brake/ turn signals. Do your '41 tail lights have dual or single filament bulbs? If they are dual filament bulbs with only two wires coming out of the housing, the bulb will get it's ground through the housing and one wire will be for the tail light filament and the other for the brake/turn light filament. In that case the ground wire will connect to the housing.