SC mechanical brake light switch project

tyro · 05-22-2010, 08:12 PM

Fed up with the silly pressure-activated brake light switch and not having brake lights on with a light foot on the pedal, I decided to add a mechanical switch paralleled to the existing system.

Picked up a long lever SPDT microswitch, P/N V7-1C17E9-048, at the local electronics store. Was not able to find this version on the 'net but did find V7-1V19E9-048 which may work as well. Cost was ~$3.

I then bent the switch lever in the proper location so that it contacts the brake lever inside the bracket.

Fabricated 1/8" aluminum plate for mounting to side of brake bearing bracket.

Mounted to bearing bracket with tek screws. Trimmed one screw short so as to not interfere with the lever inside.

Found some 6-32 nuts and screws, drilled the microswitch holes slightly to accept 6-32 screws and mounted the switch to the bracket. Spacing was done with nuts between my new plate and the switch. Adjusted switch so that when the brake pedal is pressed slightly, the switch disengages.

Utilizing the normally closed portion of the switch, I made two jumpers with faston connectors which run to the brake switch 3-pole switch on the MC. These jumpers from my new switch now connect in parallel to the black/blue and green/blue (I think those colors are correct) wires on 3-pole connector. The jumpers end up with two 'female' terminals and one 'male' each.

It's not super-pretty but it seems to do the job. As part of the job, I also added a CHMSL from Daniel Stern Lighting which cost all of $75 which was also an easy install thanks to the other threads here at Pelican on this subject.

So-so quality photos from phone and crude drawing. Note that trunk carpet is pulled back fro photos. The carpet fits over the new switch assembly without issue on my car:

carslutt · carslutt's Garage

funny i should find this post. i was unpacking some stuff in my shop and found a whole box of contact switches like the one u used and had thought of doing something like this on my car. nice work

Mitch Leland · Mitch Leland's Garage

Jess,

This has been on my "bucket" list as well... However my motivation was to get a "lighter" touch for the cruise control, but if the brake lights are also taking their time to warn the 4X4 driver on my bumper then it's a safety issue as well.

I recently bought 2 brake light switches hoping if I replaced them that this issue would go away. I'm assuming it won't???

Would this same schematic work for the cruise control? I haven't even found where the second brake light switch is for the C.C. Could you run both functions off the same micro switch?

Great post...

Kroggers · Kroggers's Garage

Nice solution - I will have to think about this as well...

tyro · 05-24-2010, 08:46 AM

Quote:

Originally Posted by Mitch Leland

I recently bought 2 brake light switches hoping if I replaced them that this issue would go away. I'm assuming it won't???

Would this same schematic work for the cruise control? I haven't even found where the second brake light switch is for the C.C. Could you run both functions off the same micro switch?

Great post...

Mitch,

Can't say 100% whether it will work for cruise as my old heap doesn't have it! That said, I see no reason why paralleling another switch with an existing switch would make a difference.

I tried the new pressure switches at first to no avail. Moderate pedal force was still required to activate the brake lamps.

Cheers,

Oh Haha · 05-24-2010, 02:02 PM

Great project. Thanks for taking the time and effort to document it.

This is next on my list of things to do to the 911.

NOLAsc · NOLAsc's Garage

Thanks for posting. I'm adding this to my project list as well. I've replaced the hydraulic switches on mine, but I'd much prefer to have those lamps light earlier than later.

andyt11 · 08-18-2011, 12:56 PM

I think this is a really neat solution and plan to do the same.

Is there any problem with drilling / tapping the alu brake booster pedestal? Whats inside and below? Are the filings and chaff going to cause any problems?

tyro · 08-19-2011, 06:11 AM

No problems drilling there. The three screws which attach the plate to the aluminum housing are known as "tek" screws, they are self tapping..cannot recall if I pre-drilled the holes or not, I suspect I did.

I'm happy to say that it's still working well!

tazzieman · tazzieman's Garage

I installed one of these as an improvement and a backup - and it works well. In trying to chase the reason why the parking brake light subsequently won't extinguish (I've searched & tried all the usual suggested fixes) , I found a good explanation as to why the hydraulic switches fail. http://www.swem.com/hydraulic%20brake%20light%20switches%20notes.htm Perhaps this also explains why even new ones fail after a short time.

My mechanical switch is wired as per the OP instructions to the front MC switch (is this #1 or #2 according to the wiring diagram? But I'm not sure why the parking brake light won't go out - maybe I will have to replace the seemingly ill-engineered MC switches just to find out? Perhaps if one switch is OK and the other isn't? The brake lights do switch on hydraulically with a fair push.