I am thinking about trying to make one of my rear brake lights function similar to Volvo's or Audi's rear fog light. Meaning that when the car is on and the lights are on I will have one of the 4 rear brake lights on constantly. I plan to do this by running a switched +12 volts to the one bulbs positive higer filament wire. I will also diode isolate it so that it doesn't light up the other lights. My questions are; do you think running a brake light continuously will have heat problems. DO you think I'll damage the bulb or housing? Has anyone all ready done this? Thanks for any responses.

 

I don't think there would be any problems with heat or wiring. But, my advice to you is, run a separate switch. You can hook up a relay so that it only turns on when the front fogs are on. A rear foglamp, as valuable as it is in foggy weather, can be quite distracting on clear nights, so this is one lamp that I would NOT have switched on all the time.

Take a look at what the VW Mark4 gang has been up to:

clicky

 

Thanks for the response. I hadn't actually thought about a switch but will now.