two electrical brake switches

[frankoporsche]

Mine is an 86 Carrera
question : why did Porsche used two electrical brake switches on master cylinder?
I disconnected one plug or other and the brake light still work...

[david.avrahami@]

probably because there are 2 braking circuits in the car

[frankoporsche]

Originally Posted by david.avrahami@

probably because there are 2 braking circuits in the car

are you sure ? is it has something to do with the front and rear of the master cylinder?

[SCadaddle]

Redundancy.

[frankoporsche]

Originally Posted by SCadaddle

Redundancy.

that could be right

[Trackrash]

Actually, it is part of the brake warning light circuit. If one of the brake circuits is down on fluid, the imbalance will turn on the brake warning light on the dash, since there is a switch on each circuit.

[Bill Verburg]

Originally Posted by frankoporsche

Mine is an 86 Carrera
question : why did Porsche used two electrical brake switches on master cylinder?
I disconnected one plug or other and the brake light still work...

[frankoporsche]

Originally Posted by Bill Verburg

Nice
Hey Bill
I only have two pole connector no middle pole on both switches stock

[Trackrash]

Some of the older cars had two connector switches.

[frankoporsche]

Originally Posted by Trackrash

Some of the older cars had two connector switches.

Hey Tracktrash
I did some testing
I disconnect one of the switches and I apply the brake pedal down and I only see just the right side of the brake light on and reconnect and disconnect other one and the left brake on not right side..
sound like each of the electric switch only work one side of the rear brake light .

[Bill Verburg]

Originally Posted by Trackrash

Some of the older cars had two connector switches.

The switch I posted above was used through '83, from '84 they went to the 2 pole design, which just has 81 & 82a, these are simple on/off switches for the brake lights.

[Trackrash]

Bill, I miss-spoke. On my '71 the switch actually only has one connector. But electrically, as shown on the schematic it has two poles, which is why I called it a two connector. '74 is the same.

So either way it looks like the OP has the incorrect switches? Or is his description of how his brake switches operate one brake light each correct?

Frank, do you have an extra unused wire connector hanging by the switches?

[frankoporsche]

Originally Posted by Trackrash

Bill, I miss-spoke. On my '71 the switch actually only has one connector. But electrically, as shown on the schematic it has two poles, which is why I called it a two connector. '74 is the same.

So either way it looks like the OP has the incorrect switches? Or is his description of how his brake switches operate one brake light each correct?

Frank, do you have an extra unused wire connector hanging by the switches?

No I don't extra unused wire connector
It must have two connector plug in ,each operate one side of the rear brake light
it is strange
I could bridge the wires together into one switches only .

[Quicksilver]

The pressure based switches are a bit failure prone. The way they fail is it takes more and more pressure to get them to turn on until they just don't work. Having the two switches in parallel is a good way to have redundancy to avoid a light failure plus as pointed out before: The brake system has redundant front and rear brake circuits so if one fails the brake lights should still come on.

The described situation where one switch does one rear light and the other switch controls the other side is either an error in testing or someone did a major hack job on the wiring harness.

[Jjason3131]

I have a 78 SC. Recently noticed the following.

1. Front Pass. parking light inoperative
2. Rear Pass running lights (back and side) inop.
3. Rear Pass brake light inop.
4. Pass side reverse light inop.
5. Turn signals work fine.

Checked fuses/bulbs. Using a multimeter, determined that there is power to the rear pass running light (back) when the lights are on. I'm alone and haven't tested brake light or reverse light circuit.

Had a mechanic look at it and he expressed opinion that something wrong with housing since when a bulb is inserted no illumination.

Any suggestions for rather testing or cure?

[dannobee]

Check the ground on the pass rear housing.

Could be a bulb or corrosion in the socket on the pass front.