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39 Stop Light Switch


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My stop light switch quits working every three years or so.  I install a new one and it works fine for a few years than stops working and then the cycle continues.   I think I once saw a post that stated that the failure had to do with the switch not compatible with modern brake fluids.  Is this true or did i just dream it? 



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Thats sad..

I think the cheap china "quality" of all the switches are the problem..

try to get another brand also with another on/off range or connectors on it , Mainly the thread is the same.

My switch i have changed 5 years ago (Standard ) an it works fine with DOT 5 Silicone fluid.

Maybe you have too much power on the switch? thatd can be a reason too.

You have DOT 4in your lines ?

Dont do that, use DOT 3 because of the agressive additives in the DOT4.

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My experience with hydraulic stoplight switches in the 40 LaSalle was that replacing the switch was an annual event until I flushed out the silicone brake fluid and installed DOT 3 fluid.  I had gone so far as to install and idiot light in the dash to indicate that the brake light wires were energized.  I now use DOT 3 in all the cars, and the brakes get flushed every other year.  I have not replaced a swich since I started that practice.


The discussion of pro-silicone/anti-silicone rages on every year.  I suspect the questions over the Kennedy assassination, President Obama's birth certificate, and the home planet(s) of UFOs will be resolved before the brake fluid debate is ended.



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I have restored a couple of cars with hydraulic brakes (one my '38 Roadmaster). I replaced all rubber parts and stoplight switches and converted them to silicone fluid. The ;38 was done 25+ years ago and I have not had a bit of problems with the stoplight switch or anything else.

The switch failure being attributed to the silicone fluid (which is pretty innert) is surprising, especially since DOT 3 is such an aggressive paint stripper.

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