Brake light switch changeout questions

'79 Dk. Green · 03-29-2013, 07:17 PM

Lucky me, I get to change out the two switches under the Master Cylinder. Got the dash cluster indicator and no longer have rear brake lights. I searched around for a previous thread of the best procedure, but no luck. Asking if removing and replacing them will require bleeding the brakes? And any tips to make the task any easier, etc? Thanks.

Mrmerlin · 03-29-2013, 08:10 PM

remove the reservoir cap and put a piece of saran wrap over the opening,
then install the cap then remove the switches
IIRC its a 24MM wrench. You will see some fluid loss so work quickly.

NOTE if you have an old master cylinder on the car dont try pressing the pedal full stroke as it will probably kill the seals inside the MC ,
then you will get new switches with your new MC

MPDano · MPDano's Garage

Also, while you have the reservoir out as Merlins describes, buy new seals that seal the reservoir to master c. It's also a know leak area. Inexpensive while your in there too.

Mrmerlin · 03-30-2013, 07:29 AM

what happens to the reservoir seals is that they trap water,
then the collars rust ,thus the smooth surface then becomes rough making the seal bad.

I would suggest that if you are installing new reservoir grommets to coat the seals with DC111 prior to installing them this will prevent water from getting in the bore in the first place.

That said if your MC is leaking here its probably time to replace it,
as its most likely over 20 years old ,
with a new MC also remove the rubber seals and coat them with the DC111

'79 Dk. Green · 04-04-2013, 03:29 PM

Thanks and from what I see, there are no leaks or other visible issues with the MC besides it's usual hard to get at location. It seems to function fine other than losing brake lights. I will seal off the cap and have the switches and tools ready for the switch swap. Will be cautious working as I don't need more issues added to the stack. I still wonder why Porsche uses such a sensitive complex system as these brake switches, when the simple on-off switch at the pedal has never been an issue in all my other cars. Plus with so many miles of wiring for everything else...

harborman · harborman's Garage

Quote:

Originally Posted by '79 Dk. Green

Thanks and from what I see, there are no leaks or other visible issues with the MC besides it's usual hard to get at location. It seems to function fine other than losing brake lights. I will seal off the cap and have the switches and tools ready for the switch swap. Will be cautious working as I don't need more issues added to the stack. I still wonder why Porsche uses such a sensitive complex system as these brake switches, when the simple on-off switch at the pedal has never been an issue in all my other cars. Plus with so many miles of wiring for everything else...

Not sure about todays paint but make sure you don't get any brake fluid on any paint. Happened to me one time and it took the paint off! Protect your fenders when doing the job.

As for switch on peddle, that would only indicate the peddle is depressed and not pressure in brake system. My thinking anyway.

'79 Dk. Green · 06-01-2013, 06:11 PM

UPDATE! I changed out the two switches yesterday (Thanks for the tips everyone) and since this car loves me so much, It didn't fix the brake light issue! AAARRGGHHH!
So if the fuse is good, the bulbs are good, all the other lights are working? The dash light used to go out once the pedal was depressed I recall, back in the good ol' days. I know of one fix to introduce the car to "My little Kalishnikov friend!" Now what? I just want to get this thing ready to sell, my heart is not in it which makes all the repairs 10 times harder to get done!

'79 Dk. Green · 06-02-2013, 07:35 PM

Anyone dealt with this? I get power to both sides of the #10 fuse. On the wire diagram looks like there is a light control unit, where in the car is it located? The "brake lamp is" the only one on in the dash. Thank you!

steve322s · steve322s's Garage

I replaced both switches still had a problem, turned out one of the new switches was bad. Do your brake lights work and the light on the dash stays on? you can make a jumper wire for the plug that goes to the switchs and this will turn the brake lights on if no other problems exist.

'79 Dk. Green · 06-03-2013, 03:12 PM

Thanks for the jumper tip, I have no lights in back and light in dash all the time. The ! light will be off.

'79 Dk. Green · 06-06-2013, 06:26 PM

Quote:

Originally Posted by steve322s

I replaced both switches still had a problem, turned out one of the new switches was bad. Do your brake lights work and the light on the dash stays on? you can make a jumper wire for the plug that goes to the switchs and this will turn the brake lights on if no other problems exist.

Reading your reply, my brake lights do not work, the dash light stays on. Same as before I replaced MC switches. Should I still try the jumper? And which color wires? Thank you.

riber.bentsen · riber.bentsen's Garage

Errrrrhm, on my 86 there is an on/off switch at the peddle. My brake lights didn't work either, went through fuses and bulbes and wires only to find one of the plugs had come off from the switch at the peddle. Put it back on, they worked.

Is this a MY- thing?