PSA: Check your brake lights. (and then get stuck trying to replace the switches)
 

My brake lights don't go on unless I use excessive pedal pressure.
I only realized this because someone informed me at an intersection.
This might be a good thing to verify on your car as it may not be flagged at your annual inspection.

If you replace the 2 brake light switches,
make sure you order the right 2 or 3 prong switch.

I began this repair today.
First remove the carpet, cover plate, cross bar, and detach 2 air hoses to access the 2 switches.

Unfortunately, both of my switches have clearance issues.
The front switch has a brake line that crosses right in front of it.
I found an image online that does not look like my brake line routing.
I suspect my brake line may have been replaced at some point, and not routed correctly around the switch.
There is no way to get an 22mm offset wrench or 22mm socket onto the switch.
Can't get an opened ended wrench in there either.

Will probably take it to the shop and report back how they approach it.
Maybe they'll need to detach that brake line.
I wonder how much play, if any, that would create.
The other end is attached to a rubber hose, that can be detached from the bracket, resulting in possible play.

I will post an update when I get this resolved,
In the meantime, I advise others to do a quick check of their brake lights!

https://rennlist.com/forums/attachme...ont-switch.jpg

https://i.imgur.com/jEAitv6.jpg

Done a lot of these over the years on both 911 and 930. While clearance is tight I don’t recall any major disassembly to replace.

brake lights switches
 

2 switches from my 87 Carrera are for sale today...reason? I changed them with new ones but found out afterwords that a burnt fuse was the problem....
See my 87 Carrera for sale listing.

One of the checks I do every so often is hit the brake pedal while in the garage to see just how hard the brake pedal has to be pressed for the lights to come on. It is scary to be out and about while driving and realize the brake light only come on in hard stops.

I have a offset box end wrench to R&R the switches. I bought it just for that purpose.

http://forums.pelicanparts.com/uploa...1615816380.jpg

I just bought the one, and not an entire set, but a wrench like this is great to get the switches off and on.

sub'd - I have replacement switches on my workbench now...

David -- this happened to me years ago, traced the blown fuse to a failing cruise control module -- hit cruise control level (even accidentally) and brake light fuse would blow - FWIW

Flex head ratchet wrench works well.

This is great guys, thanks for posting!
I literally just discussed this project this morning! This is a critical safety issue and needs to be addressed. My brake lights only come on if I am standing on the pedal-NOT GOOD!
I used to do these all day on bugs and the like but the access is not easy on the 911.

Are you tefloning the threads...etc.?

Any help, tips, tools, advice-pics etc are HUGELY appreciated!
You guys are awesome!

Teflon is for house plumbing, no need here.

The best tool appears to be a deep offset wrench 22mm.

Before your order, verify if you have 2 or 3 prong switch.

My case is unique because the brakes lines have benn replaced and not bent correctly. I will need to detach and move the brake lines, and then bleed the lines.

Cool, I was thinking maybe a crow's foot might be able to get in there too. Any recommendations on sensors (2 prong)? I have been told just to buy the german made units or the corresponding vw models because they last much longer.

Crowfoot
7/8" is 22mm

I got the ATE brand since I read that cheapo brands may leak.
Since the R&R is a hassle, I'd rather only do it once.

Or you can install an electric switch.
This way, your brake lights come on as soon as you stroke the brake pedal
(Use google translate)

https://pcxsubxci2xux76xb2ippjepji-adwhj77lcyoafdy-www-type911-org.translate.goog/blog/?idblog=10919

Oui je vois. Merci beaucoup! Était-ce difficile?

Basic rule of thumb, and there may be a couple of exceptions, 3-wire >83, SC, 84>3.2's are 2-wire.

There is overlap
3 prong. 1977-1986.
2 prong. 1984-1989.

Mechanical switch for mehttp://forums.pelicanparts.com/uploa...1615914669.png

I did the mechanical switch works great but I have this issue. 81sc with three prong switches. As soon as I press the brake pedal I get Instant brake lights but my parking brake light turns on and will not go off.
Suggestions—ideas?
Ernie

Not difficult, see electrical connection:

https://pcxsubxci2xux76xb2ippjepji-adwhj77lcyoafdy-www-type911-org.translate.goog/blog/?idblog=10915

+1 more, I add something like this to my brake lights a few yrs. ago
http://forums.pelicanparts.com/porsche-911-technical-forum/773628-mechanical-brake-light-switch-modification-78-sc.html

Dang, I replaced my sensors without much difficulty, in not much time. The original OP has a car that has some non standard lines that are in the way, so it is more complex.

It is uncomfortable getting into position in the trunk, but as an certified old geezer it was not that difficult. Two sensors, and under an hour and I was done. To build a new brake switch never even entered my mind. What ever works for you is great.

Ha. I did this after someone told me they couldn't see my brake lights. The only other thing to add - have rags handy. Some brake fluid will come out when you do the swap.

Still waiting for the switches to arrive.
Last week, my brake lights would light up only with heavy pedal pressure.
Now, they don't seem to go on at all.

Tonight, I am going to short circuit the switch connector with a paper clip and make sure the switches are the actual issue, and not wiring or bulbs.

Bridge it with a test light probe?

Sub'd

I replaced my switches today. 40 min job, and that included removing the strut brace and some of the ducting to get at the switches. Deep 24mm socket for the forward-most switch, and the offset closed-ended wrench for the one closer to the dash. Bonus: the cabin brake light went out as well! Perhaps I should have believed the light a few months back...

Since my replacement brake lines were not factory routed correctly around the brake light switch,
I will need to detach the brake lines to remove the switches
(and flush the resulting air in the lines)

So, before I did all that, I wanted to verify it was a defective switch, and not bulbs/wiring.
Today, I jumped the switch connector and verified the brake lights illuminated.
So, yes, my switches are defective. Good to know before I take apart the brake lines.
This can be checked without removing hoses, just the front plate.

Sugar wood, That’s a good test before digging in. Been following your post since I have the same issue. Good luck.

Thanks Sugarwood, I need to do a replacement myself sometime soon. they seem to need more and more brake pressure each year I don't do it.

Got the wrong switches delivered. They had a different part number and the ones I got had a 3rd plastic prong in the middle and were sized at 24mm, not 22mm. Will send the parts back.

While I was comparing, I realized this job is beyond my ability. Nothing worse than encountering stupid PO repairs that are not stock. Taking apart that brake line seems near impossible. I barely was able to seat onto the nut an 11mm flare nut wrench. But, when I got it seated, the brake line blocked the sweep path of the wrench. There is no room to seat the wrench on a different nut flat. So, I have no clue how anyone can detach the brake line. I will leave this repair up to a professional.

I have that one too, I cut the plastic off and installed it. I think its the same part other than those things...

So I went about changing switches last Friday night. Wow, about 2.5 hours later and I had it completed. The access is really difficult as others have described. I did use the sensor test lead idea to make sure they worked correctly first and they did so I proceeded.

The best way I found was to remove the vent hoses first and make the clearance you'll need for the tools. I actually found that a 23mm worked best for removal as the 22mm was way too tight to work with reasonably. The back sensor had to be turned about 45 deg at a time so it was really slow going.

Once out, the sensor BLED brake fluid! Be sure to have tons of rags and/paper towels ready to roll. My master drained approx 50% of its fluid while I changed these. That wasn't necessarily a bad thing (my fluid was awful) but it goes everywhere and isn't easy to chase inside the car (frunk). Once the mess was cleaned up, the towels and rags tossed I noticed a big difference in pedal travel to brake light activation. Previously it would only activate if you were standing on the pedal. Now it is about 40% of the pedal.

http://forums.pelicanparts.com/uploa...1616456771.jpg

That is a good photo of the correct stock brake line routing with a 90 degree bend.
Mine has no such bend around the switch. How did the switch prong get so bent ?

With your new switch, did you cut off the entire plastic cover, or just the plastic 3rd prong?
What did you use to cut off the plastic? Were your new switches 22mm or 24mm?

It Was bent reaching back to the farthest switch-this is a shot of the old switches.

I just took a jigsaw and removed the tab, filed it down a little, being sure not to go into the plastic "seal" and then connected it. One was 22 and one was 24. Not my favorite way to do it but that what I ended up with the time and I knew they'd work.

I'm trying to envision how you got a jigsaw blade around the metal prongs..

For others, here is the 3rd plastic prong in question.
Looks like the wrong part to me.

https://www.pelicanparts.com/More_Info/113945515HM14.htm?pn=113-945-515-H-M14&bt=Y&fs=0&SVSVSI=#tab1

https://cdn3.pelicanparts.com/catalo...-515-H-M14.jpg

The decision for Porsche to switch from a mechanical to a hydraulic brake switch must have been an economic choice. Ideally, you want the brake lights to energize when you step on the pedal (adjustable), not when the hydraulic pressure reaches a set threshold (not adjustable). They’re not equivalent.

There’s a large variety of mechanical switches, all adjustable depending on actuation distance. Install in any convenient location in the pedal actuation system. The brake pedal and link to the MC are often used locations.
https://www.amazon.com/universal-brake-light-switch/s?k=universal+brake+light+switch&page=2&qid=161652 4224&ref=sr_pg_2

If for some reason, you prefer an adjustable hydraulic switch, here’s a variety:
https://www.google.com/search?sxsrf=ALeKk00B8re8yhaq-AyU7TBIlvquRN475g:1616524682729&q=Mechanical+hydra ulic+pressure+switch&sa=X&ved=2ahUKEwjq7O_bh8fvAhX AGDQIHQz9CHYQ1QIwFXoECBAQAQ&biw=1403&bih=877

I replaced the hydraulic switches in mine and felt the pedal pressure was still to high for comfort. Adding mechanical switches to both my 911's is one of the best and easiest upgrades I've made.

Never considered an adjustable hydraulic switch but sounds like an interesting alternative.

Easy

http://forums.pelicanparts.com/uploa...1616531893.jpg

That blade is wider than the gap between the prongs.
Since you had to saw diagonally, I am guessing you were not able to cut it flush?
No seatment issues ?

Took another stab at this project today, but was defeated again.

The front one is basically impossible on my car, due to brake line issues.
But, I figured I would try to replace just the rear, and get the car road worthy, at least.
You just need one switch to work.

I planned to flush cutter the middle prong and make it fit.

I moved the hoses even more and I was able to get a 22mm offset onto the rear switch.
Half way out, I realized the replacement switch is 24mm.
Well, I don't have a 24mm offset wrench.
And a 24mm deep socket doesn't have clearance.
Largest regular socket I have is 22mm.

So, I aborted and tightened the old 22mm switch.
I will return these 24mm switches and pay the $70 at the dealer for the right kind of 22mm.