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This is a fix for the common "Brake Circuit Failure" message on 1990's BMW 3-series cars.OK, this is long, but it is the fix.
This is the most exciting part of the job. Go down to you local BMW dealer. Yes, the dealer. Why, because it is the only time you can get what you need with only a $10 bill in your pocket. Enjoy the opportunity, it doesn't come around often. You need to buy the Brake light switch. It is an $8 part. My dealer said that there were 2 switches. One was $11. You need the one that is $8. (If you are one of the unlucky people, your dealer has a 700% markup instead of a 300% markup, and you will pay up to $30 for the switch)
You need to remove the screws that hold the plastic panel on underneath the steering column (I think there are about 4 of them). Get a good flashlight a screwdriver and good pair of pliers. The brake light switch is under the top of the brake pedal arm, under the dash.
Examine the switch that you got from the dealer so you know how it works. The red tab, when pressed down, locks it into place. SO, the last step before buttoning everything down is to press the red tab down to lock the switch in place. The best way to get the old switch out is to grab your pair of pliers and break off the red tab or the entire white button. Then it is easy to pull out once you have the wiring harness disconnected.
To make things easier, I would park the car on a lever surface so you can have the car in the on position. In order to get the old switch out, you need to have the brake pedal depressed as far as possible. If the car is off, the brake pedal stiffens up and makes removal of the switch rather difficult. The switch is engaged when the pedal is released, so the pedal needs to be depressed to release the switch.
Here are the details:
1) remove panel below steering column
2) climb under dash, upside down
3) depress brake pedal
4) remove wiring harness from switch
5) break off the red tab or the entire white button
6) remove switch from its bracket
7) pop in the new switch
8) depress the red tab on the switch to lock it into place
9) connect wiring harness
10) re-install panel under the steering column