So I have been taking advantage of the nice warm weather we've been having and got the 53 C600 MH mostly rewired.
started out as just gonna replace the light switch that broke and a couple of leads off the ignition switch that snowballed out of control and now mostly all of the wiring has been replaced. should have just made a nice clean harness or ordered one but no, it looks like a huge rats nest of new wires under there now.
Anyway. To the question, Initialy I was not getting any current through the MC pressure switch until I cleaned the contacts up with acetone and emery paper, then they worked but only when I really pushed hard on the brakes, (they are a little spongy, need to bleed the vac assist brakes and all to make sure it's good) the running light s were also working fine. but after I finish hooking up my turn signals (completely seperate lights and lines etc) the tail lights are coming on but I was not stepping on the brake and the running lights are turned off.???
I assume the MC pressure switch is bad (stuck) making the contact so the lights stay on?? but if so wouldn't they be really bright like when stepping on the brakes? or maybe it's just a weak contact?? confused and really didn't want to have to swap that pressure switch and go through bleeding all the lines.
Maybe I need to go look at how I wired the light switch again....
If you are using the standard dual element bulb the inner filament is the brake light and the outer filament is the running light. You should be able to tell which filament is iluminated. A further test would be to disconnect the wires from the brakelight switch and connect them together. Does the inner filament light up?
The pressure activated brake switch on these old pieces is well known for both internal failure and external failure. Contaminants, corrosion to the outside terminals lead to the failure you initially experienced. Like ND said, internal crud leeds to failure of the switch. DOT three brake fluid being hygroscopic draws moisture which exacerbates the problem.
These switches should activate with very little pressure and turn off when the pressure is released. You want the switch to activate when you roll up to a stop with the brakes applied easily so as to notify following drivers of your intentions. It is also necessary that the switch turn off when no pressure is applied or you will have a dead battery. The switches are cheap.
Thanks guys, it looks like maybe I should just install a mechanical lever style switch, I was initially thinking I would do that but then it started to work, so back to square one. I don't really want to re-bleed the entire system otherwise I might try a pressure switch again.
I've had no problems with the pressure switch. The problem I see with a mechanical switch is that there is relatively small movement of the parts of the linkage when the brakes are properly adjusted, and light braking. At the pedal pad, I doubt there is 1/2" of movement after adjusting my shoes, and that is the point of most motion. You can't put a switch there, obviously. Mechanical switches I am familiar with need more motion than that. I suppose you could loosen the pushrod and make more play down below, but I like them the way they are.
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