Fixing parking brake warning light switch

[speedking]

Here is a simple fix to a problem that can be important, since proper working of the warning light is needed to pass state inspection.

When I got my 1979 911 SC, the parking brake warning light never came on. Here is the behavior it should have exhibited: when the ignition was switched on, but the engine is not running, it should be on. When engine is started, it should be on if the parking brake is on, and should be off when the parking brake is off. The goal of this light is to prevent people from driving with the parking brake on, which can overheat the rear brakes and lead to loss of brake efficacy.

In my case, the bulb was missing from the warning light. The red plastic panel on the dash pops off with a bit of light prying. The bulb itself pulls straight out, and is easy to replace. There is no need to go under or behind the dash in order to replace the bulb. Easy fix.

There is a switch inside the parking brake that was not working in my case. To fix it, it is necessary to remove the carpet. You will probably need to remove the passenger seat as well.

There is a flathead screw on the passenger side of the parking brake assembly. When it is loosened, the parking brake switch can be moved up and down. If the switch is working, it is adjusted by first setting the brake on two clicks "on", the adjusting the height of the screw until the warning light just turns on. This procedure must be done while the engine is running.

There is a brown wire that sneaks into the back of the parking brake assembly. It connects to the switch, which is really a shaped plastic part with an electrical contact strip on it. Make sure that this wire is connected (as described below).

To fix the switch, or reconnect the wire, the parking brake assembly must be unbolted from the floor. There are three hex bolts that come off easily. There is no need to detatch the heater cables or the parking brake cable. But the long bolt that serves as the pivot for the brake handle and the heater handles will need to be removed, to create some slack. Therr are a bunch of friction disks between the heater handles; be careful not to drop them in the hole in the floor, and note their order for reassembly.



Once there is slack on the assembly, unscrew the flathead screw and remove the switch. If it is not connected to its wire, now is a good time to reattach it. The following pics show the switch after removal, including a pic that shows its part number.




If the switch does not work, regardless of adjustment, the contacts may not work. To fix this, pull the brake handle all of the way back to reveal the copper "elbow" on the underside of the assembly. This copper connector is meant to touch the copper on the adjustable switch. On my car, the elbow had lost its bend, and was not making contact. I bent it with a pair of needle nose pliers. The pic shows the contact after it was bent; it works reliably in this configuration. The pic is showing the underside of the assembly. Bolt it all back together, and it will work.



The following pic shows the friction disks, nut, washer, and heater fan switch unit in the order that they were taken out of the car. If you are missing a friction disc, look inside the hole in the floor; it may have been dropped there during a previous service.



I hope this post is helpful to you. I have benefitted from this forum so much that I wanted to give back. Happy motoring!

[poorsha]

Nicely done.
Thanks for the tip.
Keep em coming.
Happy new Year

[Sicklyscott]

Nicely written. I need to take this as my light won't go off. It's either the contact / switch or it's the circuit board itself. This looks like an easier fix.

[bugstrider]

Just would like to say thank you for this post. I followed your lesson plan and seem to have remedied our particular issue. I have dialed in the adjustment per your points and have a question.

You state:

"adjusting the height of the screw until the warning light just turns on."

Are you referring to the height of the switch or the actual depth the retention screw is dialed in? I say this because I found that i could fine tune the point the brake light would come on by how tight or loose the screw is threaded in.

Again, fine wright up and thanks for sharing.

Cheers Trevor

[universeman]

Height of the switch. Not threading the screw all the way will cause the switch to vibrate/rattle all the way to the bottom of the slot. Screw is designed to be tightened fully, hence the star washer on it.

[keitho64]

Thank you for sharing an excellent write up!

[Bill Douglas]

Thanks. My '79SC has never had a working parking brake light either. That reminds me; I need to put the car on a hoist, remove the back wheels, and adjust the parking brake after a friend drove 20 miles with the hand brake on

[cellison]

on my 79 930 if the emergency brake switch is working and it is adjusted correctly and the warning light stays on, what is my next step? the brake switches on the master cylinder? when one of the brake light switches on my 88 was bad the brake light warning light didn't come on.

[blg5035]

Bump for a great how-to.

I was able to bend the copper "elbow" without removing the pivot bolt. You might be able to lift up the parking brake assembly enough to see the elbow with an inspection mirror. I fit my hand under and pinched the elbow.

[B61]

the copper"elbow" broke on my brake handle...
is this easy to replace? Its looks rivetted?
B61 - Bruno - Bredene

[Vincent Hill]

This Thread sure Helped me. Yes I knew the Assembly Of the Heater Levers But not the Brake somehow my wire to the Brake Light Switch got pulled loose. So I need to fix that and have a light working again thanks to you

[Steve F]

I need to do this as well, been putting it off! Thanks

[isby]

I just finished this project, which took all of about 15 minutes. Great directions from speedking -- many thanks. I had enough slack when I pulled up the brake assembly that I did not need to remove the long bolt that serves as the pivot for the brake handle and the heater handles. Cleaned up the contacts, bent the copper elbow a bit with some needle-nose pliers and adjusted the height of the switch. Brake warning light now works perfectly - great fix for a very annoying issue.

[AlKidd]

I know this is an old thread brought back by isby but mine is a nogo and this came up in a search. Am I correct in assuming the brown wire goes to ground when the copper strip makes contact? If correct this means I can test the circuit by grounding the wire? I tested my bulb and its ok but before I tear into the handle assembly Id like to know the circuit is working.
Al

[cortney]

AlKidd - I am working on the same problem now. I found this thread and have the same question as you. I believe that is how it works, making contact with a ground turns on the light and breaking contact turns off the light.

I will check when I get home tonight before ripping into the handbrake assy.

[cortney]

So after digging a bit in the car - I found that the PO had disconnected the bulb & housing from the harness behind the dash because the handbrake warning light is stuck ON. I guess I have the opposite issue that others are having so I might have to chase down a grounded wire somewhere.

[isby]

Cortney - I had the same issue - the light was stuck ON. It turned out that it was the position of the switch. As noted above, there is an adjustment screw on the handbrake assembly that controls the switch position. Once I loosened this screw, I was able to adjust the height of the switch to where I could get the light to turn off as the parking brake handle is lowered.

[spuggy]

I wanted to thank the OP - my handbrake warning light just suddenly stayed on, and this write up made it very easy to get everything apart. Although his warnings weren't quite enough to stop me fumbling multiple things into the abyss under the handbrake console, heh.

Turns out my contact bow was intact but entirely the wrong shape; took finding a clear picture of a new one (from an old For Sale ad on Early 911S) to figure out what it should look like.

Note the bow is a straight line after the rivet holes, followed by very nearly a right angle::



Mine was like 45 degrees after the area supported by the handbrake lever - guess 250,000+ miles on the tub had taken a toll, and it'd just deformed slowly over time until it made contact with the brake off... Bent it gently with needle-nose pliers until it looked like a new one and it Just Worked when bolted together again... I'm guessing this was expected - the "switch" was in the very lowest adjustment position when dismantled, and I put it back right at the top.

Gotta love a $0 fix...

[HarryD]

I had an issue with my brake warning light.

Turned out to be a failed switch on the master cylinder that tells you when the hydraulic brake system has failed.

Before you go to the heroics of adjusting the parking brake switch, pull the electrical connector off of the switch on the master cylinder and see if that fixes it.

[MarkWard]

Hello, working on the same. 1980 SC. The contact that is riveted to my hand brake cable is broken. Found the end in the tunnel. Nothing there I can bend to make contact to the switch. Circuit tests fine though. My factory manual does not seem to discuss this. Is there a repair kit similar to pictured above? The part number seems to be just for the rivet. Thank you. Mark

Edit, found this part number for the contact bow. Pelican shows it NLA. 901 613 523 20