Brake Warning Light Won't Turn Off

[kenzinger]

Hi All,

A little background - I just purchased an '83 911SC. I had all of the brake calipers rebuilt and new pads put on a few weeks ago. I don't believe any work was done on the parking brake

I then drove with the parking brake on (doh!) for a few miles and the brake light wouldn't turn off after disengaging the brake. My mechanic pulled the speedometer, reset something inside the dash and the brake warning light went off. Great!

Just a few days ago, the brake light came on and it won't turn off, but this time I didn't drive with the brake on.

I've searched through the forums for potential brake warning light causes and have found it could either be

1) Bad brake light pressure switches on the master cylinder
2) Bad parking brake switch
3) Ground strap on transmission(?)

#1 - This is usually accompanied by a delay in brake light turning on when applying the brakes, correct? My lights exhibiting no problems in this area.

#2 - I don't believe this is the case because the parking brake switch operates perfectly when the brake warning light isn't on permanently

#3 - Is this really a potential cause? Does anyone have a picture showing me which ground strap to replace?

Does anyone have any tips on how to troubleshoot this issue? On my Jeep, I am more than happy to throw parts at problems until they go away because they are cheap. The switches aren't expensive either but I'd rather not dig all the way back to the MC if I don't have to.

Right now, I plan to use the key method to reset the light (Key on, positive battery terminal off, positive terminal on, key off) but curious where to go from here.

Thanks!

[Bill Douglas]

My SC occasionally does this and by just disconnecting the battery for a minute fixes it, but by the sounds of this you have tried that. You could also try jumpering or disconnecting the two wires that go to the cap on the master cylinder filler, mess about with those to see if it's the switch there causing troubles. Mine's a bit fussy in regard to fill levels. Also I can get an air bubble under the filter that sits under the filler cap, which reads as a low level. Good luck.

[kenzinger]

Originally Posted by Bill Douglas

My SC occasionally does this and by just disconnecting the battery for a minute fixes it, but by the sounds of this you have tried that. You could also try jumpering or disconnecting the two wires that go to the cap on the master cylinder filler, mess about with those to see if it's the switch there causing troubles. Mine's a bit fussy in regard to fill levels. Also I can get an air bubble under the filter that sits under the filler cap, which reads as a low level. Good luck.

I didn't think that there was any sort of level sensor in the MC on the SCs. Am I mistaken? I did check brake fluid level and it looks to be full.

[walt]

I became so frustrated tracking this issue down I finally disconnected the light. Possibly a short somewhere. I don't believe their is a level sensor on my 82 SC.

[john walker's workshop]

Old brake light switches can do it. The speedo out and reset thing was an O2 light reset. Nothing in there relates to a brake warning light. Are you seeing a red light on the speedo or by the radio or on the console?

[Bill Douglas]

Originally Posted by kenzinger

I didn't think that there was any sort of level sensor in the MC on the SCs.

Mine's got a switch that has (guessing) 10 mm up and down movement that is part of the filler cap. Under My car is a Euro 1979.

[stevie 77 930]

I went through this on my 83 SC as well a few months ago......

1) I removed the brake light/seat belt warning light from the dash.
Disconnected from harness to reset. Replugged the harness, brake light stays on. (i did not reinstall the warning light until i knew i had resolved the problem)

2) Then 2 new brake light switches on the m/c. Reset seat belt/brake light again Brake light still on

3) searched for a new/used (different) warning light. found 2 tried all of them. Brake light still on

4) finally, took the parking / emergency brake handle. New switch on the brake handle... I found the issue. a bent grounding tab that is riveted to the handle, it was not making correct contact with the switch. Fussed with the tab and re-bent it so it makes contact correctly. It took a couple of attempts to make it right , but ultimately got it.

For the sake of prosperity, i disconnected-reconnected the seat belt/emergency light from the harness once more.

Finally, turned on the key. Both seat belt/emergency light were illuminated. After a few seconds the seat belt light went out and i when i released the emergency brake, the brake light WENT OUT !
I reinstalled the seat belt/brake warning light back into the dash.... Done.

[kenzinger]

Originally Posted by stevie 77 930

I went through this on my 83 SC as well a few months ago......

1) I removed the brake light/seat belt warning light from the dash.
Disconnected from harness to reset. Replugged the harness, brake light stays on. (i did not reinstall the warning light until i knew i had resolved the problem)

2) Then 2 new brake light switches on the m/c. Reset seat belt/brake light again Brake light still on

3) searched for a new/used (different) warning light. found 2 tried all of them. Brake light still on

4) finally, took the parking / emergency brake handle. New switch on the brake handle... I found the issue. a bent grounding tab that is riveted to the handle, it was not making correct contact with the switch. Fussed with the tab and re-bent it so it makes contact correctly. It took a couple of attempts to make it right , but ultimately got it.

For the sake of prosperity, i disconnected-reconnected the seat belt/emergency light from the harness once more.

Finally, turned on the key. Both seat belt/emergency light were illuminated. After a few seconds the seat belt light went out and i when i released the emergency brake, the brake light WENT OUT !
I reinstalled the seat belt/brake warning light back into the dash.... Done.

This is really helpful! I'll start tracking some of these down. I'm a bit concerned though, as when I disconnect my battery, the brake light goes out for a while and the parking brake portion works exactly as expected.

The only unusual thing I've noticed is that when the lights are on, the difference in brightness between the running lights and the brake lights is negligible. Is that expected or does that potentially point to an issue in the MC switches?

[kenzinger]

Originally Posted by Bill Douglas

Mine's got a switch that has (guessing) 10 mm up and down movement that is part of the filler cap. Under My car is a Euro 1979.

I'll have to pull the cap off and take a closer look. Thanks!

[kenzinger]

Originally Posted by john walker's workshop

Old brake light switches can do it. The speedo out and reset thing was an O2 light reset. Nothing in there relates to a brake warning light. Are you seeing a red light on the speedo or by the radio or on the console?

The warning light is for the brake - it's odd as I watched him pull the speedo and then reset something and then the brake light went out. I reset it using the battery/key method and it went out for about a day but came back.

[kenzinger]

Originally Posted by walt

I became so frustrated tracking this issue down I finally disconnected the light. Possibly a short somewhere. I don't believe their is a level sensor on my 82 SC.

This looks like a common solution but I would love to have a warning if there actually were a problem! And I am a bit forgetful, so having the parking brake warning work would be helpful as well.

But it may come to this...

[stevie 77 930]

There is no level sensor in a 83 brake fluid reservoir.

If your seat belt/emergency brake light goes out after disconnecting the battery and then re-illuminates, perhaps the circuitry in the warning light board is faulty. Perhaps is time to look for a replacement in order to rule out the possibility its not working. Have a look at these posts as reference

Parking brake light always on

SC Brake Warning light problem

Or send the unit to Tore Bergville for repair
https://www.bergvillfx.com/index.php/services.html

[Jonny H]

Originally Posted by kenzinger

The switches aren't expensive either.

A word of warning. Never fit the cheap VW brake light switches. Two reasons:

1) The PO of my car fitted VW switches - the type that are a pressed and crimped metal can. On annual inspection, the tester stood on the brake pedal and the plastic end separated from the metal can - pedal straight to floor with complete loss of that brake circuit.

2) Not all VW switches are wired the same as Porsche ones. Although the brake lights will work, the brake warning light will never go out.

[kenzinger]

So, I've discovered that the previous owner put the wrong bulbs in the tail lights. They were single filament and so it showed no difference between lights on and brakes applied. I've replaced them with the correct dual filament bulbs, is there any possibility that the brake warning light could be triggered by this?

I've reset the brake warning light but I'm doubtful that it will stay off.

[stevie 77 930]

certainly worth a try....

[kenzinger]

Originally Posted by stevie 77 930

certainly worth a try....

The brake light has been gone for a full day with several trips out and about town. I'm hopeful that this has been fixed by replacing the single filament bulbs with dual filament!