88' 528e brake light sensor

1988 528e. When I turn the car on, the "check light"...(forward panel) and the overhead "brake light" are on. Pressing the reset
button(overhead panel) or pressing the brake pedal extinguishes the forward panel light but not the overhead light. I've checked all the light connections in the trunk area, cleaned them, installed ALL new bulbs....problem still exists. I bought the car with this problem. I've already replaced the rotors, pads and brake sensors (they were due) This is also an intermittent problem, more often than not.....
2) the cruise control only accelerates when pushing the cont fwd...does not engage or maintain speed...not sure where to start but was wondering if the brake problem is tied.......Nathan
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Try replacing the bulbs with the silver-base Osram bulbs. Sometimes the brass-base bulbs trigger the brake check light due to higher resistance. Alternately, check the brake bulb seats on the rear lights for water/grease/anything conductive that might create a electrical path bypassing the bulb. Don't forget the 3rd brake light in the rear window. I use a reflective surface (window, another car, anything that the lights will light up) to check the brake lights are all working when I'm in the car stepping on the brake. Just fixed a similar problem on my '86 535i. There was conductive grease in one of the brake light holders creating a path that set off the brake check light.
Bill in Omaha '86 535i
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will
that
P.S. The brake check light is ONLY triggered by the brake light electrical system, not the brake hardware. It responds to the electrical current/resistance in the brake light circuit. The brakes (master cylinder, fluid, lines, pads, rotors, calipers, wear sensors) have no effect on the overhead check light.
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I've replaced ALL the bulbs in the car from a bmw parts dealer with OEM parts......and...as I said, I have already cleaned ALL the connections, every last one of them, every light in the car...except the interior......also, today, replaced the brake light switch......problem still plagues me.......
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1988 528e. When I turn the car on, the "check light"...(forward

I
will
There
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So then the overhead light stays on regardless. I wonder if the check circuit board in the overhead piece is faulty. Did you by chance check the wiring harness connections for the lights in the trunk? Mine were slightly corroded. They are under the fabric/cardboard piece adjacent to the taillights. If the check board is good, then somewhere a high resistance is being created, maybe corrosion.
Bill in Omaha
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Depending on the model you have to press the brake pedal to reset the brake light warning. (i.e. to do something which brings the lights on)
On newer models you can only start in Park and only select R or D by pressing the brake pedal.
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brake
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The overhead Check Light stays on until you initially depress the brake pedal or press the button on the overhead panel. Either depressing the brake pedal or the test button overhead tests the circuit and if ok, the light goes out.
Bill in Omaha
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no, it doesn't go out.........that's whats wrong........so, not ok..........still looking, did the brake light switch today. I think I'll take all my light parts off and put them on a new beemer.......lol........
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The contact plates that hold the lamp sockets should be carefully cleaned and dielectric grease put on them. Likewise the sockets should have grease in them.
If this does nothing, then it's time to open up the black box in the trunk. You will find is full of reed relays, and either the relay contacts are bad (and the reed can be replaced) or there are cold solder joints.
It takes only a TINY change in current to set these things off. --scott
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"C'est un Nagra. C'est suisse, et tres, tres precis."

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