| Back up to a wall and watch the rear-view mirror as you press the brake 15-20 times. Make sure that the lights light up EVERY time you press the brake. If they fail to light even once, get a new brake light switch that fits behind the pedal arm.
The switch is inexpensive, but it is a bit of a PITA to get at. Replacing it involves standing on your head, and small hands and small tools are helpful. You have to crush the old switch to get it out, which tends to bend the bracket, so be sure to straighten the bracket to center the switch on the brake pedal arm after you snap in the new switch.
On one of my e36s, I had some trouble with continuity in the tail lights, so I removed the assemblies (you have to stick a pry bar in through the bulb holes in the body and pry to break the rubber seal loose from the body). I then ground off the tips of the plastic pins that hold the sockets in place on the tail light assembly, and then soldered the pins to the metal traces. The pins are just dry-crimped to the traces, so loosness and corrosion are possible. After soldering the pin connections, I used JB Weld to epoxy the plugs back on over the pins. I also buffed up the traces around the bulb sockets with steel wool. The whole job took about an hour, plus time for the epoxy to dry before reassembly. With that and a new brake light switch, I eliminated brake light warnings for the past several years.  |