Brake Light Switch Secrets

While replacing my clutch master cylinder I broke the top off the brake switch. Many small brass metallic parts and springs flew all over the front compartment, so I ordered a $30 replacement. It only had two wire fittings instead of the four on the original, so I ordered the four fitting replacement for $130.

In the mean time I experimented with the two prong version I had on hand. First, the threaded nylon shaft is NOT located by either the nylon nut that comes with it, the small end cap that snaps on the end or a backing nut on the far side of the mounting hole. The mounting hole itself is threaded. It is a firm fit and does not really require even the front nut to hold it in place.

With the new switch dangling I connected the two large wires, turned the ignition switch on and observed the brake lights came on. I then removed the terminals and screwed the switch progressively into the mounting hole, testing from time to time if the brake lights went off when I reconnected the terminals. When they did I simply added a half turn and left it be. The end cap would be helpful since it would provide a limit to how much you could screw in the switch, but it won't fit through the mounting hole.

Now the bigger surprise. The two smaller wires to the old cap were still dangling in place. They are for the turn signals. And once the brake wires were disconnected from the old cap the turn signals worked. I simply wrapped the old cap in electrical wire and left it dangle till the four connector switch arrived. It seems clear to me the four wire system is intended to show a brake light burn out by deactivating the turn signals.

 

I too just replaced my switch. Naturally, the 4 wire switch was shockingly more expensive than the 2 wire but I found one on ebay under the alfa crossreference number from a guy saying it'd been on his shelf for 20 years. $29 with shipping.

I also tried to dissassemble the switch and had the springs and little contacts fly all over eventually. That is one complex little mechanical switch. One of the contacts was completely worn through--not fixable at all although I DID manage to reassemble things.

I figured the extra 2 terminals were for the error center checklight in my center console.

 

On my 86, I replaced with a 2 prong. Brake lights work, just get a warning on the pedestal (Yellow Bar and yellow light) when depressing the brakes. Actually, I think it was the opposite. Yellow Bar and yellow light on all the time except when pressing the brakes. So wired the 2 wires together to get the previous. Didn't want the yellow light on all the time....

 

Two conditions:

Pedal up (no brakes): Green supplies 12V (ignition on only) via the red/black to the to check control ecu.

Pedal down (brakes on): Green supplies 12V (ignition on only) via 1) itself to check control ecu, sunroof switch and (via the hazard switch in off position) to pin 49 of the blinker relay, and 2) via red to the check control ecu.

I think.

 

I feel for you. That brake switch looks very flimsy. I removed it before taking the clutch master off. When I put it back on, I was very nervous about over tightening it so it would not snap in two.

You did an amazing job drilling out the threaded holes on the clutch master cylinder. Maybe you can modify a brake switch? Maybe start off with one with the correct contacts?

I am not sure if this one would work:

Alfa Romeo 33 90 Sprint 1 7 Brake Light Switch New | eBay

We'll all be watching you.

 

You mentioned alfa crossreference number. Do you have it handy? Is it already on the crossreference list?

 

When my brake light switch broke on my 85 Mondial I replaced it with this $9.20 switch from Amazon. I had to change the wire connectors, but otherwise fit perfectly and has worked flawlessly for two years so far.
Amazon.com: URO Parts 4A0 945 515A Brake Light Switch: Automotive

 

I have a new four pole switch around here someplace. However, I ended up using the old one that sprouted micro parts all over the place. The brake light innards were still working. I figured the other two connectors simply provided a closed circuit for the turn signals.

In some sort of weird way those complicated internals are supposed to detect a bulb out and keep the turn signals from flashing as the signal for such a condition. I think. OK. So now I might not know if one of my tail lights are out. How often does THAT happen. Right now I simply have those two smaller connectors connected to the part of the original switch that separated. Put some black electrical tape over it and they have been dangling there for about two years.

I actually do not know if the two smaller wire connectors, the ones that are now in closed circuit on the dangling extra piece, would need to be attached to the four post unit in a particular left/right position! I can just see getting it wrong and needing an entirely new fuse box or some such. It works and I am not going to fix it!

 

Any one advice how to disassemble and assemble a new stop light switch?

 

get a drink first

 

I know it's an old thread - but having just snapped the top off my brake light switch, I'd though I'd add in some part cross references I've found for the original 4 terminal switch that is fitted to my 1984 QV. Taken from a manufacturer's website I've found the following:
Intermotor also make an OEM type under their part number 51681, and can be found on Ebay as new old stock for less than £10 delivered... They appear to be slightly different, but basically are the same part.

• ALFA ROMEO 113306517700
• ALFA ROMEO 60515008
• FERRARI 119439
• FIAT 5954516
• FIAT 5964877