Last week, I noticed that my PS brake light was on, even when the car was off. I did not think anything of it, and figured I could get it fixed whenever I had some spare time…then my battery died! Even with the batter dead, the light stayed on. I pulled numerous fuses, and none worked to turn it off, so I disconnected my battery (which did the trick). I have not jumped my car yet, but was wondering if anyone had any thoughts? I thought it might be the brake switch, but since it is just ONE light, and not both, am not sure that would be the problem. To note: I have a 2010 Mercury Mariner, 37k miles, and had a UHaul hitch installed about 3 years ago. DR brake light goes on when brakes are pressed. Help!
You need an auto tech to help you out. The brake lights are typically wired to a single circuit, so there must be a cross-circuit short causing the one light to stay on. Did they install an aftermarket light converter (also known as a logic circuit) to the tail light wire harness to give you a trailer connection? On my 2000 Explorer, it came with a built-in trailer circuit that just needed an Explorer-specific trailer light connector to plug into the factory harness. The logic circuit was built into the truck wiring and controlled by a separate fuse. My 1990 Toyota needed an aftermarket logic circuit to be added. A malfunctioning logic circuit may be back-feeding the PS brake light. Especially if one of the fuses you pulled was for the tail light circuit and the DS light stopped working.
It could be a right turn signal light that won’t shut off due to a malfunctioning multifunction switch or a short in something else live shorting out to that turn signal wire.