brake warning light

[Paul Crowther]

My brake warning light is on. I've read that fluid level is not a factor, and if it's due to a dual system failure, the light comes on when brake is applied. Other possibility (likely) is the parking brake lever switch. Not much info on where it is, but it's got to be around there somewhere.

Any tips?

Paul

[schoward]

There is a reset procedure for that light. Do a search. One way is to unplug and plug-in the light from behind it (go in thru clock hole), letting it sit unplugged for 20 seconds or more before reconnecting. There is a capacitor in the light module that needs to drain hence the delay in reconnecting. I did this to mine over 2 yrs ago and no issues since. There is a procedure where you turn key, disconnect battery, etc but I do not know it cold. Do a search; I know Ive seen this discussed before.

[Paul Crowther]

I failed to mention that this was the 82SC.

Paul

[holtjv]

Originally Posted by schoward

There is a reset procedure for that light. Do a search. One way is to unplug and plug-in the light from behind it (go in thru clock hole), letting it sit unplugged for 20 seconds or more before reconnecting. There is a capacitor in the light module that needs to drain hence the delay in reconnecting. I did this to mine over 2 yrs ago and no issues since. There is a procedure where you turn key, disconnect battery, etc but I do not know it cold. Do a search; I know Ive seen this discussed before.

I have the same problem with my SC but have never tried the method above--I will tomorrow though. I did the process suggested by John Walker ( I think) with turning the ignition on, disco the battery, etc. I have forgotten it, too, but it didn't work anyway. Since it's your SC there's no brake sensor to trigger the light (iirc) so it's not that, unless I'm mistaken.

[Rick V]

Hey Paul, drop me a line, I may have time on sunday to swing by and reset the light.

[gblumenstock]

I had a similar issue on my 79SC. I tried the reset procedure and that worked for a drive or two. The real solution was replacing the two sender units on the master cylinder. I think that the failure light come on if the two sender signals do not match one another within a certain value (suggesting loss of one of the channels). Over time, I think that they can corrode or drift out of spec. I do not remember this being pricey or difficult to fix.

I bought the parts from our host and used a 24mm wrench to break the 25 year old seal once I had drained the brake fluid from the system. Put it all back together, new fluid and bled the system. I have not had a problem since.

Hope this helps.

GB

[Paul Crowther]

Rick,
Tried to PM you, can't figure out how. 589-4295.
Sunday is no good. This afternoon (Sat?) Not urgent.

What do you think about this master cylinder stuff? Ya know, I had the car checked out by someone last week (yearly physical) and when done the light was on, so I wonder if something got knocked out of place at the master.

I am ready to disassemble the hand brake lever to check the switch there.

BTW, when hand brake is let down the light dims ever-so-slightly, but remains on.

Paul

[gblumenstock]

I would try the reset procedure to see if that will clear your trouble. Also make sure that the handbrake is all the way down. If these both fail to solve your problem, I would than try more invasive things like I suggested in my previous post. Always do the easy things first.

GB

[Paul Crowther]

Da dah..
Fixed.
Undid the plug behind light.

And plugged it back a minute later. Did you think I left it unplugged? Now we'll see if that's the end, or if it comes on again later. If so, I guess I'll replace the switch in the handle. More of a pain but still doable.

Paul

[holtjv]

Originally Posted by Paul Crowther

Da dah..
Fixed.
Undid the plug behind light.

And plugged it back a minute later. Did you think I left it unplugged? Now we'll see if that's the end, or if it comes on again later. If so, I guess I'll replace the switch in the handle. More of a pain but still doable.

Paul

Do me a favor and follow up on this if it recurs. Same thing with me--unplug then re-plug and it's fine for a few days then back to being stuck on.

Thanks..Jack

[janz]

My 86 has the brake pad sensor light and the brake light to the left of it. The brake light started coming on after I rebuilt the parking brakes (complete brake job all around) and i chased this for weeks checking the little things. On mine there is a sensor for brake fluid in the reservoir cap, it has a little rod that activates using some sort of float device in the reservoir, I cleaned the contacts in the cap and made sure the rod moved up and down, this wasn't the problem. Tried the reset, ignition/battery disconnect and that didn't do it. I decided to rebuild the shifter bushings and removed the drivers seat to do it only to find out the brake switch is on the passengers side so i didn't bother with it then. After the shifter rebuild the brake light would only stay on like every other time when releasing the parking brake. Wasn't happy with the shifter so adusted it at the coupler a few times until it was just right. Guess what, the brake light goes out each time I release the parking brake now. What does one have to do with the other I don't know nor do I care but that annoying red light is off when ever the parking brake is off now. I am glad i don't have to pull all that stuff apart in the parking brake handle encloseur as the car has AC and climate control and I hate removing the seats becuase some nit wit before me destroyed the allen head bolts (where the socket fits in) and each time I try to buy enough to replace them they only have 1 or 2 in stock, so I replaced the really bad ones. Guess I'm venting about idiots that should not be given any type of wrench.

[Paul Crowther]

Jack,
Will do.

A local Porsche friend advised me that what is happening here is that the switches on the master cylinder may be going. There's two on the master, and they monitor fluid pressure in the system. You can see them from above the master, in the trunk.

If they're replaced, obviously the system must be bled again.

Paul

[3.2 CAB]

If it is actually the handbrake lever switch causing the light to stay on, it can be adjusted to the correct placement. There is a little bolt/screw that holds the handbrake switch in place, in the curved channel it sits in. You loosen the retaining bolt/screw just enough so you can slide the switch either up or down in its track, till you have it adjusted so when the handbrake handle is released and at its lowest position, the switch is no longer making a closed circuit. The switch is just completing a ground circuit for the light.

I have seen some 911 handbrake housings that had been removed, and the wire that went to the switch had been pinched between the housing and the tunnel, by this wire being pinched, it created the ground to complete the circuit. It did not matter what the handle or the switch position was. If you look closely at the handbrake mounting plate, you will see a little hump towards the rear end of it, this is where the wire runs through between the handbrake housing mounting plate and the tunnel. Good luck!! Tony.

[darryl92cab]

I had the same issue on a newly purchased 82SC as well. All was fine until one day, the light came on and stayed there. I did the ignition reset and that did indeed make it go out, but then it was always out...even if the emergency brake was ON. Just a few days ago, I moved the car from outside to inside and sure enough, it's back!! I think I may have had my foot on the brake when I started the car and that may have triggered it. I have the two switches for the master cylinder, so hopefully, that will fix the problem. Hope to get those installed this weekend. I'll post the results here...hopefully the light will come ON when the brake is actually ON too!

- Darryl

[Paul Crowther]

Well. This thread is back alive. Amazing. I have a VERY competant mechanic, and the first time the light came on was when I picked it up after he did work on the car. Last year. I reset it without fuss when I got it home.

I picked the car up today after having suspension work done. The light was on again! He wasn't there when I picked it up so I couldn't bust him, or ask what the heck he did to cause it to happen TWICE.

I guess the clock comes out tomorrow so I can reset it again.....nuts.

Paul

[Westy]

I had this problem a few years back in my '81SC. I'd forgotten about it. I forgot that I'd unplugged the light. So I went out and just plugged it back in. The light came on,,,*****!!

Now,,,I remember when it started, sometimes I just played with the E-Brake (get ur head outa the gutter), and it would go out. Obviously, at least to me, it's the switch. Soooooooo, if I take out those 3 bolts, can I just pull up on the handle to get to the switch? I don't even care if I just disc onnect it, then if the light comes on that means I have brake issues developing. Anyone? Anyone? Anyone?

[Paul Crowther]

Sorry to hear about your light coming back on after you plugged in. Something is probably wrong with one of the valves in the master.

I'm happy to report that after resetting mine it remained OK.

Of course, the car is back in the shop with a problematic air leak, so I guess it will be on again when I get the car back! Can you spell "I may need a new air box"??

Paul

[ybn533]

Hi,

After a big search I did the reset process suggested by John Walker. Worked for a day and the light is back on.
The hand brake switch should be fine because it worked for a day.

So, what left is to replacing the two sender units on the master cylinder?
Pelican Parts - Product Information: 113-945-515G-M323

Any other ideas before I order it?

Thanks
Yaron

[wwest]

That was one of the early indications that my battery was being over-charged, brake light latching up due to over-voltage. Remaining on until battery was disconnected, but then repeating shortly thereafter.

'78 Targa

[86 911 Targa]

Here's the PC board CKT.

Hope this helps: