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.

 

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

 

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!