Low pressure to brake light switch??

[sandiego]

Tail lights don't work. Pulled one of connectors to brake light switch on master cylinder, jumpered the contacts, and got tail lights. So assumed the switch was bad. So put in a new one and problem was not solved. Is it possible even thought the brakes work well that somehow I am getting insufficient pressure from the master cylinder to the switch so the switch doesnt work? Would air in the system cause this? Thanks.

[86 911 Targa]

Originally Posted by sandiego

Tail lights don't work. Pulled one of connectors to brake light switch on master cylinder, jumped the contacts, and got tail lights. So assumed the switch was bad. So put in a new one and problem was not solved. Is it possible even thought the brakes work well that somehow I am getting insufficient pressure from the master cylinder to the switch so the switch doesnt work? Would air in the system cause this? Thanks.

We don't have your model/year, however I went through this with our 3.2
a while back.

After shorting the brake light switch harness (brake lights o.k.),
I replaced both brake light switches in the redundant system,
and all is well.

The brake lights will work with one switch.

However, I did not see any serious brake fluid loss during this repair.

Just a few drops.

Have you checked the fluid level on top of the master cylinder?

and, how long were the switch ports open?

Good luck,

Gerry

[Quicksilver]

Originally Posted by sandiego

Tail lights don't work. Pulled one of connectors to brake light switch on master cylinder, jumpered the contacts, and got tail lights. So assumed the switch was bad. So put in a new one and problem was not solved. Is it possible even thought the brakes work well that somehow I am getting insufficient pressure from the master cylinder to the switch so the switch doesnt work? Would air in the system cause this? Thanks.

Probably the pressure is fine but the switches are toast. If it is a pressure switch there should be 2 of them. They fail often.

I added halogen brake lights so instead of the lights saying "stop" they now say "STOP!". To help with the general unreliability and the added load, I added a relay to the system.
(Gods own brakes and wimpy, wimpy tail lights...)

[rnln]

Not sure about your car but mine has 2 switches very close to each other. The design is that if one is working, the brake lights will work but mine doesn't work that way. I tested after replaced one switch, problem was still there. After both were replaced, problem gone. I didn't dig deeper after that.

Originally Posted by sandiego

Tail lights don't work. Pulled one of connectors to brake light switch on master cylinder, jumpered the contacts, and got tail lights. So assumed the switch was bad. So put in a new one and problem was not solved. Is it possible even thought the brakes work well that somehow I am getting insufficient pressure from the master cylinder to the switch so the switch doesnt work? Would air in the system cause this? Thanks.

[sandiego]

Heres some additional info:
Car is an 1987 Carrera.
Fluid level is correct.
Switch replacement was several seconds so very minimal fluid loss.
Car does have two switches which according to the schematic are in parallel so even if one fails open circuit and the other is good then the lights should work as designed. If one fails closed circuit then the light would be on all the time (in Accessory or ON mode).
I guess I will try replacing both switches but if it works I won't understand why!!

[rnln]

who knows, might be a bad/defective first switch. If so, then you might fall into the same situation I was in.

[86 911 Targa]

The brake lights should work with one switch.

Here is the CKT, and, the switches fail in the open (normal) position.

Also, an offset wrench for the rear switch (closest to the window) will save a lot of time.

[Jesse16]

Similar failure with my 87. Was taking more and more pressure to make the brake lights come on and I was concerned I'd get hit. Around town in gentle driving, I could brake and they never light up. Just replaced both switches and problem solved. Tells me that the diaphragm in the switch gets less responsive or the contacts inside the switch move somehow. Pressure is pressure at the top, air or fluid for pushing on the switch. Can't see how trying to "pre-wet" the tip of the switch when installing would do anything. You could have and all air brake system if it wasn't so spongy. If the pedal isn't spongy, you've got pressure!
Can always go the more "project" route and put a regular switch on the brake pedal at the cluster.