Brake light switch failure?

[gary griffin]

I have two cars with the dual master cylinder kits and the brake light works fine in the 1940 LaSalle but not in the Cadillac 1942-6719    The installer forgot to install a tee for the brake light switch so we took out a section of front brake line from the master cylinder forward and added a tee and brake light switch and it did not work, so we replaced it with another new one and it did not work either. The fluid reservoirs are full but we did not bleed the brakes in case we have to change the switch again. There is power to the switch but none coming from the switch when pressing the pedal. Could air in the system cause this? I doubt it as it would exert the same pressure as the fluid would?  Any suggestions will be appreciated.

[Bobby B]

Gary,
Jump the switch first just to make sure it's NOT the switch and therefore it's a blockage of some sort (or air). I've never had a problem like that unless the switch itself was faulty.
                               Bobby

[gary griffin]

Bobby,

   We checked the current coming into the switch and held a volt meter on the other side of the switch and activated the pedal, also plugged it into the harness and the brake lights did not come on. I am wondering if the duality is the problem. The rear brakes seating before the front brakes receive fluid pressure? There must be something in the master cylinder to prevent that though.

[Steve Passmore]

Air will compress Gary whereas fluid will not so it could be the air doing it especially if you didn't bleed after fitting a 'T' in the line.

[Bobby B]

Gary,
Check up with what Steve said. The only time there would be a proportioning valve would be if you had front disc and rear drum. The purpose of the brake proportioning valve is to equalize the braking pressure between the rear and front brakes. If a driver brakes hard, the brake proportioning valve coordinates more pressure to assist the front brakes so that the rear wheels do not freeze or lock. Technically, if everything if operating correctly, you should have even pressure in all the lines exiting the master regardless of how many "Tee's" you have in the system, unless you have air trapped in the line somewhere. Was the MASTER Bled first? If it wasn't, you could possibly be bleeding till the cows come home to get the air out of the remaining brake lines. Some cars are take longer to bleed than others, due to the various positioning of the components.  Make me happy first and remove the two wires off the switch and jump them to see if you have brake lights. I have gotten bad switches right out of the box. Take nothing for granted in today's aftermarket…..
                                                                                                      Bobby

[Bill Ingler #7799]

Gary: I was taught many years ago that whenever you work on a wheel cylinder or remove a brake line, always bleed the whole system. On a side note on the brake switches. The only new brake switches being made are from Mexico. These I have found have a high failure rate. I have had a new switch right out of the package that was bad. The old NOS switches like by Cole-Boston or Niehoff are the switches you should try to use. Getting harder to find plus expensive.  Bill

[TMoore - NTCLC]

I agree with Bill (as usual) - I have had a high failure rate with the current aftermarket brake light switches.  Test the switch under known pressure to rule that out first (switch with the known good LaSalle to verify that the suspect switch works).  If that is verified, then I would agree that you might possibly still have air in the line.   I bled my lines over and over - had a great firm pedal, excellent brakes, but no lights with a new switch.  Put the old one back in, and viola - brake lights at the lightest tap of the brake pedal.

[TJ Hopland]

I have never had good luck with pressure switches especially when power brakes are involved.  Seen it many times where the lights may come on at first when you are coming to a complete stop but then will go off again unless you really keep your foot down hard. 

I have also had a lot of issues getting them bleed out properly which could lead to the not reliable / desired operation.   It does not take much air to soften the operation.   Unscrewing the switch to bleed the T is just about required and is a real hassle.  On one car before I finally gave up on it I even tried to pre fill the switch with fluid before installing thinking that perhaps there was air in the switch itself.   Maybe the internal switch design has changed and there is more internal volume that does not really bleed?

What I finally ended up doing was fabricating a simple L bracket that I hose clamped to the steering column that had a simple hardware store switch on it.  I used a small piece of hose around the shaft of the switch to help act as a bumper for the pedal arm so it was not slamming directly into the switch.   It also helped my pedal travel issue in this case. 

[gary griffin]

Thamks for the good advice, I do not think I will bother to finish bleeding the brakes until I can find a GOOD brake light switch. Does anybody know of a source for the Cole-Boston, or the Niehoffer that Bill mentioned.

[gary griffin]

I found a Wagner FC 7715 in my spare parts box, and it was labeled "Made in America" I will assume it means USA?  I am searching for a glove box light switch and will keep on looking for a replacement brake light switch from the ones that Bill Ingler suggested. Bill has been looking over my shoulder and saving my bacon during my restoration. Hopefully I will be able to pay it forward someday. The guys on this forum have all been  a great deal of assistance.

[Steve Passmore]

When you say you want a glove box light switch what type are you looking for Gary? The ones I have on my original cars where Mercury operated and never seem to work for some reason even though they still have the Mercury. Its still possible to buy some other type of Mercury switch to adapt to it or is yours more mechanical?

[Paul Phillips]

I have the same situation on the glove box for my 41-60S. I found a 'ball bearing' type of tilt switch that looks like it can be repackaged in the housing from the original mercury switch. Should know in a few days how well that will work.

Paul