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Brake fluid reservoir level switch operation and troubleshooting
The BRAKE warning light in the instrument cluster on our cars will tell us one of two things when it is lit up:
1.) Your parking brake is engaged, or
2.) Your brake fluid reservoir level is low
Both of those two conditions will make the same warning light come on. The parking brake warning is done by a plunger style switch mounted to the parking brake lever assembly. The low fluid level warning is done by a float attached to the bottom of the reservoir cap. Both of these switches turn the warning light on by completing their circuit, i.e. when the switch is made, it completes the circuit to ground and 12v is sent to the light bulb in the instrument cluster to turn your warning light on.
The reason I mention any of that is because my reservoir fluid level switch has not worked the entire time I have had my car. That changed today though!
Here is the switch: http://store.delorean.com/p-7480-flu...indicator.aspx
Notice it is NLA at $0.00 so you can't buy a replacement. Not through Houston anyway.
My brake warning light works for the parking brake and I tested the wiring at the fluid reservoir to confirm it was fine on the car side. I jumpered the two connectors and sure enough the brake light came on. So the problem is in the switch and not the car's wiring.
The float monitoring level is not all that unlike the one used in the fuel sender. In theory anyway. It will not give you an indication of the level, only the warning light that it is low. So you get the fuel low warning light but not the fuel needle telling you how much is in your tank. The float is attached to a stem where the float part is sitting down into the fluid in the reservoir and the top of the stem is up in the cap.
The top of the switch is supposed to have a black little bubbly button that you can press on to test your low level warning light. This can be confusing as it is not electrical in any way. The little rubbery dome you press on with your finger is really only physically pushing down the stem and float and forcing it low, which in turn should complete the circuit and turn the light on.
How does it complete the circuit? It does it by way of a small washer that is clipped to the top of the stem and moves up and down with the float. When it is all the way down, the washer comes in contact with the two electrical spade ends within the switch, completes the pathway to ground for the 12v, and turns the light on in the instrument cluster.
Guess what happens when there is corrosion all over that washer? IT DOESN'T WORK!!
I realized that washer was in there almost by accident as I was cleaning the switch up and trying to figure out how to get into the guts of it. I suspect the stem is supposed to come out the bottom, but since my little rubbery button on top was long since cracked, the stem came up that direction. I took some sand paper to it and cleaned it up best I could and wouldn't you know it, the little light came on!
I put it back together and tested it dipping into the brake fluid and the light went out, then back on again if I lifted it up and out of the fluid. The little button top still works as all you're really doing is pushing down directly on the stem to force the float down and the washer to come into contact with the two leads.
I took some pictures of things when they were disassembled so you can get an idea of what is going on. Maybe that will help someone else wondering why theirs doesn't work or even help to understand how that little system is supposed to work.
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