A buddy has suggested to me that perhaps the brake warning light switch (plastic switch with two prong connector that screws into the distribution block) may be supposed to have a spring internal to the switch which would push the plunger back down (when the shuttle is centered as it should be) rather than relying on gravity alone to let the plunger drop back down. If yes, all the switches I have are bad (no spring action but plunger free), this might explain the unusual amount of difficulty I have had trying to get the warning light to stay out after centering the valve. Can anyone comment?
Now, for those of us that think they can take the switch apart and fix the spring, how stuff would you say the spring is? Like a ball point pen spring or is it fairly stout?
I have a question about the Brake Light Warning Switch for a '70, which should be functionally similar to the '68/'69…
I just bought one to install, as mine was missing. I figured I would check the switch before I installed it, so I put the DVM on it and reading from pin to pin the switch is closed / shorted / zero resistance. When I measure while pushing the plunger in I get the same readings pin to pin; zero ~ closed switch. So now I’m trying to figure out exactly how the switch functions in the circuit…
Looking closer at the pins, I can see that there is a metal connector between them: i.e. the pins are a single metal piece. So they will always read zero ohms between them!
When you push in the plunger it appears to come into contact with a portion of the pin piece. My theory is that this would short the two pins to ground through the plunger and brake distribution block, changing the resistance in that circuit and lighting the “Brake Warning” light in the dash.
This would also explain why the switch itself is plastic ~ so the pins stay “ungrounded” until the plunger touches them.
Does this sound at all correct?
*It also looks like I will also need to rebuild my distribution block. When I removed the plug that was in the switch port I had a bunch of fluid leak out ~ so the o-rings are shot. Oh well, so much for my planned 10-minute job, LOL!
Yes, your description of the switch is correct. The only thing I have to add is there is some other function the two pins have in the wiring, as in it completes a path or something (I never dug in far enough to figure it out for sure), otherwise they would just use one pin. But yes, the pins are isolated until the plunger comes up and grounds them to indicate a brake hydraulic problem.
Also, regarding the spring, a lot of times the old switch can be made to function again by squirting WD-40 (or your favorite stuff) up into what the plunger recesses into and you can most times work the stuck spring loose which will then return to spring loading the plunger. This was the problem that both of the switches I had (and was inquiring about in this and a thread on MCnet). I did what I have described and got them working again (although I put a NOS one in Isabel anyway).
