Adjusting brake light ?

damian911 · 03-24-2006, 09:09 AM

Hello friends, recently my brake lights are not coming on when the pedal is depress, this was a gradual effect...the pedal had to be further and further depress'd before now it doesnt engange at all....I have a 83sc, i looked at the pedal cluster and dont see anything there to adjust, can anyone help me????

jasonlee · 03-24-2006, 09:22 AM

Same thing happened to me. Its time to replace the brake light pressure switches. There are 2 of them, and you probably need to replace both. they are about $8.00 each from our host, and its a simple do it yourself job. Good luck

damian911 · 03-24-2006, 09:31 AM

great thats cheap compared to everything else...haaaaa....so can u tell me where these switches are so i can do this myself??? thks damian

jasonlee · 03-24-2006, 09:39 AM

they are on the master cylinder you may need to remove some ducting , but its pretty straight forward. If you don't already have a Bently manual, or at the very least a Haynes or Chilton...get one

drl911 · drl911's Garage

I replaced my pressure switches last year for the same reason, however, no significant improvement was noticed. It could be the aftermarket switches found at the local parts stores do not function the same as new OEM switches. In any event, I eventually installed a simple mechanical micro switch to the back side of the brake pedal near the pivot point and wired it in parallel to the pressure switch. Now I have "instant" brake lights!

Good luck,
Dan

911pcars · 03-24-2006, 12:18 PM

"In any event, I eventually installed a simple mechanical micro switch to the back side of the brake pedal near the pivot point and wired it in parallel to the pressure switch. Now I have "instant" brake lights!"

This is the way the early 911 brake lights were energized. With an adjustable microswitch, you can set the ON threshold to whatever you prefer (even connect a momentary switch for those wishing a closer look at your rear bumper @ 60mph). Sometimes new technology isn't what its all cracked up to be.

Sherwood

Bill Verburg · Bill Verburg's Garage

964 and 993 also use a microswitch at the pedal

jasonlee · 03-24-2006, 02:10 PM

microswitch, thats a great idea, Anyone have schematics on how to set it up...Sorry for the hijack

damian911 · 03-24-2006, 11:57 PM

no hijack here, gonna try switch my switches first and if that doesnt work i may try the new method too....thks for info friends.....damian

movin · 03-25-2006, 01:48 AM

Ditto experience here. I replaced mine only to find I still need to push way too hard to activate the brake lights. Definitely a hazardous condition and potential liability for all parties involved. What a stupid piss poor quality POS design by Porsche again. I'm wondering what next?

Gunter · Gunter's Garage

Damian:
There are thousans of SC's with OEM pressure switches that work very well. Be prepared to bleed the system when installing the new switches.
If you don't know the state of your brakes, this may be the time to do them. Good luck.

damian911 · 03-25-2006, 08:51 AM

dumb question??? why does it need two switches?

Gunter · Gunter's Garage

No question is dumb.
Porsche uses a dual system: The front brakes have an independent circuit, the rear ones have the other independent circuit.
In case one circuit fails, you still have some brakes left.
The MC has two lines coming out: One for the front, and one for the rear. (Therefore 2 switches)
Get a Bentley SC Repair Manual, you'll love it!

movin · 03-25-2006, 09:57 AM

The problem persisted after the usual pressurized power bleeding I always do to all of my vehicles. I do remember the same problem about 30 years ago with a Volkswagen I had. Turned out a bad batch of Bosch switches had QC problems and I wasn't the only one to see this which leads me to think there is a problem with these switches lately and the manuafacturer may not know this. Bottom line, you shouldn't have to stomp down like Godzilla to activate them and the guy behind you doesn't get adequate warning, and he may just take you to the cleaners if his attorney finds this out.

damian911 · 03-25-2006, 04:14 PM

so does mean both switches are bad? or just the rear switch? what does the switch for the front brakes do? I thought the switch just triggers the rear brake light, do they do a other role, say for the front?

rnln · 03-25-2006, 07:19 PM

drl911,
I just replaced mine a while ago. Before I did, I was thinking of the Mechanical switch too but can't find any good one for it yet, and can't have this problem for long (don't want to get rear ended). Now, I still want the mechanical brake since many posted the pressure switches won't last long anyway.
Could you post some pics of where you install it in? And which/where you get the switch?

Gunter,
reading your response I got confused. When I replced mine, I try to operate the brake light with one switch hook up just to see what is going on here because I also wonder why do we need 2 switches. Guess what? Brake lights weren't turn on. I tried each sowtch at a time and have same result. As long as I hook both in, brake lights are on no problem. So I thought the circuit needs both switch to be complete.
Don't get me wrong. I am not saying you are wrong but just my confusion from the conflict between your reading from Bentley manual and my experiment.

Thanks.

911pcars · 03-25-2006, 11:10 PM

"....because I also wonder why do we need 2 switches."

As Gunter says, the factory designed the system in case one of the dual circuits fails; the other continues to operate the brake lights.

Looking at the wiring diagram for an '81-82:

http://www.pelicanparts.com/911/911_Parts/Electrical/911_electrical_82SC_Part3-1.jpg

.... both switches are wired in parallel from source voltage (Fuse 15, grn/bl) to the brake light circuit. Thus, either switch (given sufficient MC pressure) should be able to energize the brake light circuit.

rnin,
You can check for system voltage (~12V) at the grn/bl wire at each brake light switch with a voltmeter; and with the brake pedal depressed (with enough force to close each switch), source voltage should then appear at each blk/yel wire leading to the brake light branch circuit. With the circuit wires disconnected, you can also check switch continuity with an ohmmeter (pedal up; pedal down).

Not sure why BOTH of your brake switch connectors have to be installed before the brake lights go ON as each switch is independently wired. Did you try each switch independently? And neither one energized the brake lights?

Looks like they started using the dual MC brake light switches in '78.

Sherwood

rnln · 03-26-2006, 03:41 AM

911pcars,
Yes, I tried each switch independently and it won't light up the brake lights. When both are connected, lights work fine.

Gunter · Gunter's Garage

The SC wiring clearly shows that they should work independently; not just on the rear brake lights, but also for the interior brake warning light.
Hm.....Have to think about this.

damian911 · 03-28-2006, 08:48 PM

well guys i replaced one of the two switches (the easy one first) because auto zone only had one also, and shazam! the rear brake lights now work!.....i still dont get it why there are two when one can put it out of commision....thks for all the info....Damian