I installed a new head unit over the last couple days, and had the car battery unhooked during this time. After getting the head unit installed, everything seems to be working properly but now my brake light on my dash is stuck on. Brake fluid is at the max line and brakes and parking brake are functioning as normal. When I installed the head unit, I just grounded the parking brake cable from the head unit that keeps videos from playing while you are in motion and stuff. Does the head unit communicate this back to the car in a way that would cause the dash light to stay on, or is this just a coincidence in timing?

 

Most parking brake indicator light circuits I've seen are active on a connection to ground.

Meaning, when the parking brake is off, the switch is open and the indicator light circuit is not a complete circuit so the lamp doesn't light. Then, when the parking brake is on, the switch is closed and the circuit's connection to ground is complete and the indicator light turns on.

On these modern cars, the parking brake switch signal is an input to an ECU, which then decides whether to turn the indicator light on and off.

So, if you grounded the actual parking brake switch wire in the car, you are telling the ECU that the parking brake is always active.

There are DVD bypass circuits at A@mzon, etc. that would allow you to watch videos while you do not have the parking brake active. However, this function is getting more and more difficult to override, as GPS for navigation can be added as a trigger on whether to allow viewing functions, too.

 

I only grounded the parking brake connection from the head unit. I didn’t do anything with the actual parking brake, the switch, or any wires from it.

 

OK.

But the description I replied can still help you in your diagnosis. I would start with the parking brake switch - see if that is working: measuring open/closed whether it is activated. If the switch is OK, then see if there is a short in the wiring to the parking brake switch.

If you haven't already, download the FSM and use that to guide your diagnosis, as well.

 

I'd probably just pull the bulb, but I'm lazy

 

If you check the Service Manual you will see that the BRAKE light can receive a ground from 4 sources: the parking brake switch, the brake fluid level switch, the alternator, and the microprocessor in the instrument cluster (for ABS related problems). Grounding the connection at the head unit will not effect the BRAKE light, so it has to be one of the 4 signals above.

 

I tried to pull the switch off the base of the parking lever, but it didn't seem to want to come out. I couldn't see in the FSM how to actually remove it. However, it seems that wiggling it and pushing down made the light go off anyway