[scarceller]

I also have failed switches, my brake lights do not come on till I really get on the pedal. I just got my new switches in and decided to review the schematic of how the Brake light circuit works and I think I may now understand why they may be failing.

First, as already pointed out by DRACO they seem to fail because of arcing due to current load. The 2 bulbs most likely pull 5-8amps (Will measure this to be sure soon). You can see in DRACO's pictures that the right side contact is very pitted and damaged it looks like the result of arcing across that contact.

After a review of how they are wired they do in fact carry all the current to the lights across the 2 switches (meaning no relay is used).

Then to make matters worse they are wired on the 12V side of the circuit , meaning the switch cuts the 12volt side and the bulbs are wired to ground. From Electronics theory 101 I was taught this is a bad idea. It's always best to have a switch wired on the ground side if it is to carry any excessive load. Not sure of the physics here but the bottom line is that cutting the ground side reduces arcing across contacts. You often find most automotive switches (like the door pins and such wired to ground for this reason.

So before I jump the gun and go for a mechanical switch on the brake pedal I've decided to put 2 new switches in the Master Cyl along with a Normally Open 12V 30amp relay. I'm going to wire one side of the switches to ground then the other side to the relay coil. Then I'll apply 12V to the other side of the coil and simply have the switches ground the coil to activate the relay. The the relay main contacts will activate and apply the 12volts to the brake lights.

This will insure no more that 1/2 amp ever flows through the 2 switches and should keep them in good shape with very litttle or no arcing.

One other point about Incondencent bulbs is that when they first light up they draw at least 2 times momentary current than when they are fully lit. This means that these switches can see momentary current as high as 10amps or more when the switches first close.

One other idea would be to drive the brake lights not with a relay but rather with a PNP hi power transistor setup as a switch, sort of a solid state relay with no contacts. We use these types of circuits often in Electronics to drive motors or pick valves in Plant Floor Control (factory and manufacturing plants) where we can not tolerate any arcing because of flamable gases in the area.