Hello All! I have an interesting brake light issue on my build. I apologize ahead of time that the components I'm working with aren't all traditional, and if that breaks the rules let me know and I'll pull this down. Brand new Painless wiring harness, using it with the suggested new GM style light switch. I have this mocked up with a FlamingRiver GM style column. Out front I have parking lights/signals and headlights. In the rear just two tail lights with integrated turn signals. Headlights and front park lights/signals work great. Headlight dimmer switch works. In the rear the turn signals work as they should, I apply the brakes and they illuminate as they should, hazards work as well, but ONLY if the headlight switch is in the off position. In park lights and/or headlights full on, my brake lights are on full bright. I try to signal and the front indicators work but the rear lights are still on full bright (brakes applied brightness) and no signal. I temporarily wired a light to the 3rd brake light wire simply for troubleshooting and it works as it should. Only illuminates when brakes applied so that's telling me the brake light switch is working (also because the tail lights illuminate when the headlights are off). All grounds checked and re-checked. Ran temporary grounds from the tail light housings just to be 100% sure there. Sorry for the essay here but wanted to provide as much info as I could for you guys. Basically, my tail lights are on full brightness when I turn my lights on (temporary 3rd brake light is not) and everything works normal when they are off. None of the lights are LED. It's been an all day head scratcher. Thanks in advance!
sounds like you just have the rear filaments wired wrong. You have the bright one connected to the tail light wires, and the dim ones connected to the turn/brake wires.
Jim's on the right course, but I think there's more. First, I'll bet there's three wires coming out of the rear light ***embly. These should be ground, taillight, and brake leads. If the tail was connected to the brake lead, brake to the ground lead, and the ground to the tail lead it would act like this. Dis***emble the light and remove the lamp, then verify that the ground lead is connected to the lamp shell, not either of the lamp contacts. Make sure it's connected to ground. Once this is verified, then try both other leads on 12V to find the brighter output which will be brake/turn. Do disconnect that third brakelight.
THIS! DO as he suggested. If memory serves right the third brake light wiring completely byp***ed the turn signal switch. On a traditonal hot rod or custom about the only thing you might want it for is if you had a truck with a flatbed that you wanted to put a second pair of lights in the back of the bed that were tail and brake only like a lot of the big trucks have.
If the brake lights only work with the headlights off, find a other source to power the brake light circuit.
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