Pelican Parts Forums - Mechanical Brake Light Switch Modification

Pelican Parts Forums (http://forums.pelicanparts.com/)

- Porsche 911 Technical Forum (http://forums.pelicanparts.com/porsche-911-technical-forum/)

- - Mechanical Brake Light Switch Modification - '78 SC (http://forums.pelicanparts.com/porsche-911-technical-forum/773628-mechanical-brake-light-switch-modification-78-sc.html)

Quote:

Originally Posted by RSBob (Post 8454811)

Follow-up: brake warning light is on in cabin and cruise control will not engage. Looks like I will need to use g150driver's mod.

Update: Just did the mod and the brake warning light is now off and with my new LED brake lights are now instant ON! Just a touch of the brake pedal, like a modern car, and they are on Bam!

Now just need to see if cruise control works.

I just did the switch mod to two cars, one with cruise one without. Im having brake warning light issues. Did your cruise work after you installed the diode harness?

So I did the switch addition in the original post, but now I've got the brake warning light on.

I'm trying to wire up the harness in post #21 but I can't understand a few of the connections, since the poster's diagram is such low res. He also has the relay included in the picture (but no switch) and the switch in the diagram (but no relay). I've started drawing a diagram, but I need someone with more brains than me to finish it. I do know that my Green/Blue wires going to the OEM plugs are the 12V ones. I'm thinking those are the wires that get the diode, but maybe not.

Here's my (lousy) diagram.

http://forums.pelicanparts.com/uploa...1524245256.jpg

Quote:

Originally Posted by 911pcars (Post 9300995)

It's been awhile, but the issue when adjusting the mechanical brake switch on early 911s is - there is no obvious height adjustment of the switch.

The pin that transfers pedal motion to the master cylinder can be adjusted for overall length. This can provide a limited brake pedal engagement adjustment range for e.g. easier heel-and-toe actions.

However, the large washer that bears against the switch lever arm is normally clamped against the pedal end of the pin. Changing the pin length also affects when the switch contacts close relative to brake pedal movement.
http://forums.pelicanparts.com/uploa...1475263803.jpg

If increasing the arm length for higher pedal engagement, this results in delaying switch activation (i.e. contacts close - brake lights ON) until further downward movement of the pedal stroke.

A simple solution is to install washers under the switch mount so the lever is in a better position relative to the large washer.

Another "solution" is to install spacers on the driver side of the large washer (spacer-washer-nut). This allows the large washer to be placed along the short threaded section of the pin so it can bear against (and release) the switch arm at a more desirable pedal height.

Sorry. Don't have a pic of the suggested spacer-washer-nut arrangement, but hopefully the description suffices.

Sherwood

Never saw this reply. What is not shown in above pic is the brass portion of switch which has threads and a nut to adjust length to allow for instant on lighting regardless of pedal position.

I just bagged all the mods and added two new brake light switches on the master cylinder and put in two new regular bulbs and called it good. It all works fine like it should.

I have tried the standard recommendations to improve the brake light response time on my ’87, including new switches and cleaning contacts, etc., (as you did, RSBob), but I really was not satisfied with the result: there just is no way to ensure activation, in the stock system, with only light application of the pedal. I have found myself actually over-actuating the brake pedal at stop lights or in stop-and-go situations in order to ensure that the brake lights come on. This is not the way it should be. I therefore decided to install the mechanical switch, and you can see here what I accomplished (I did the install over the last weekend). I am very pleased with the results, and I finally feel like I don’t have to worry about this issue. Like others, I wired it to run in parallel to the pressure switches, so it is a redundant system (I essentially piggy-backed off the second circuit switch). You can see in my photos that I went with a small bracket attached directly to the booster mount housing to hold the switch, but then I added a “protection” bracket to prevent it from being knocked off when throwing things into the trunk.

http://forums.pelicanparts.com/uploa...1524492094.JPG
http://forums.pelicanparts.com/uploa...1524492094.JPG
http://forums.pelicanparts.com/uploa...1524492094.JPG
http://forums.pelicanparts.com/uploa...1524492094.JPG

Very robust, I think, though perhaps not as elegant as others without my limited fabrication skills and equipment could achieve. I really want to thank Craig_D, Arne2, and everyone else’s inputs on this topic. Great ideas, and a fine example of community innovation. Much, much appreciated.

Don't sell yourself short, Lyle. that looks great.
so glad to have found this thread. what a sweet mod.

I plan to do this mod to my car as well.
Here is are some other setups others here have applied.
http://forums.pelicanparts.com/porsche-911-technical-forum/993041-mechanical-brake-light-switch.html

I like walts idea.

When I did the mod and switched to LEDs, no matter what I tried, the cruise control wouldn’t activate because it looks at voltage through the brake circuit. Since I used to use my cruise control on 500+ mile drives losing it was not an option until I changed over to EFI which totally did away with cruise. Grrrr

Brilliant! Thanks for the share. Did you then wire it into the existing leads off the old sensor? Which one? Or does it matter?

Quote:

Originally Posted by thsupernge (Post 11263558)

Brilliant! Thanks for the share. Did you then wire it into the existing leads off the old sensor? Which one? Or does it matter?

Thanks! Yeah aside from my solution, there are a few other great ideas in this thread.

To see where I stuck the blades, look back at this post. I just pressed the blades from the electric brake actuator into the existing leads for the hydraulic actuator. So I have redundancy, in case the electric actuator fails.

http://forums.pelicanparts.com/porsche-911-technical-forum/773628-mechanical-brake-light-switch-modification-78-sc-2.html#post8374868

When I did this upgrade I used a Double Male-Female adapter on the brake light switch leads to achieve the redundancy function.