Okay, my memory has gotten as rusty as a Plymouth in the 6 years since my car was restored. Right now my brake lights don’t work. There is power to the switch, if I unplug and cross wires, the lights come on. This tells me the switch has failed. What is involved in replacing it? If I un-screw the switch, will the M/C drain out, necessitating a bleed of all brake lines?
Several people have recommended I “simply” add a modern switch inside the car, under the dash, activated by the brake pedal arm.
First I hope to learn the answer to my first question. Then I would appreciate any tips on adding the modern under-dash switch (what manufaturer, what location to mount switch). 
My memory is rusty too. I replaced these pressure brake switches years ago and I don’t think brake fluid leaks out but I can’t remember either.
On the modern brake light switch; I have one on my car. I want to say I got a '70’s volare switch but not sure or I got a universal push button type for a couple bucks. It just has a button on it that the brake pedal arm contacts. I think it was on the “Help” rack in the auto parts store.
What I did is made a bracket that new switch is attached too and then attach bracket to something near brake pedal. You gotta make sure brake pedal arm makes good and correct contact with switch button, so what I did is C clamp the assembly to a piece by the brake pedal. That way you can move it around to find good contact before you drill holes and bolt it.
I just went out and looked. Switch is still C clamped. It’s just a small, maybe, 1" C clamp. It works so good I left it that way 
YES, FLUID WILL LEAK OUT. But not really a big deal, use shop towels to keep the DOT3 off the finish. be quick and you may not have to bleed the system. If some fluid did splash on your paint. Just wipe it down with a wet cloth. and also dry the area.
Ahah, thanks Rick!
Roger - I did my monthly check of FWDLK email and on 6/28 they’re talking about brake light switches. You might want to check it out. Something about different threads, etc. and one person uses a Harley Davidson switch??? Do that, and then a person can amaze a Harley guy by telling him “I’ve got Harley parts on my '59”.
I’ve got Chevy parts on my '59 (Monte Carlo brake calipers and hoses, I believe, thanks AAJ ) but I don’t tell anybody 
Roger,
More often than not, after changing the switch you will introduce a small amount of air into the master cylinder. Generally, this will bleed out by simply pumping the pedal several times. The original switches are getting harder to find, different diameters where the unit screws on, and an adaptor fitting may have to be used. Some folks are converting to a mechanical switch, those from early '60’s Mopars seem to work quite easily from what I have been told.
—John
Funny that this question is here, i was away for a week and when i went to start the Plymouth, the battery was totally dead, to the point that it wouldnt even take a charge, after getting another one i found my brake lights to be on, further investigation showed that fluid is leaking for the stop light switch, so am i to understand replacing the switch will solve this??
Bob
Bob,
probably a typo, did you mean to say fluid is leaking FROM the brake light switch?
This would be odd, as it is a sealed unit.
Do some more investigating, and get back to us. I have a NOS switch here I would be happy to sell you for my cost!
Yes it is, i can see it dripping down from the switch, i unhooked the wires and found them to be wet.
Okay, to me that’s wierd, because that means the plastic innards of the switch have failed. With our cars, anything is possible!
I’m worried that sediment in your car’s lines or reservoir have clogged the switch, causing it to stay “on”, then maybe the pressure of one more pedal push cracked the weakest link.
I’d recommend you flush the reservoir, and replace the switch.
The odd thing is that talking to other “old” Chrysler guys, they’ve never heard of this happening. the master isnt that old, but the switch is older, it was on the car when i got it and when the master went in 2006, the same brake light switch was used, but ill see about getting another switch tomorrow and I’ll let you know what happens…
Bob
Bob - I get those switches from the local NAPA dealer.
Dick.
what was the outcome of this?
lol, you know i forgot to put an update about this on here…
No one around here (parts stores) had the switch, and the guys that i call when i need something like this were all on vacation, so at a local cruise night some of the guys had noticed that they hadnt seen my Plymouth recently, i usually drive my Chev 1 week and the Plymouth the next week, so i told them about my dilemma and one of them said, i may have one of those at home, sure enough the next day he brought it to me but i had to get an adapter for it, so this problem has been fixed since last weekend, funny thing since, all the parts guys that i either called or emailed came back from vacation and of course they all had the switch available!
Also, i did find out that its not uncommon for the switch to develop a leak such as mine did, but everythings fine now and i didnt have to bleed the brakes either!
Bob
I was curious, so I put my old switch in the vise and tried to develop a crack in it.
Not possible! So I am baffled how your switch developed a leak. Myterious.
Hey Matthew - Fixed the Brake Lights, my fried Ed said to try bleading the master cylinder, I had Steele push the brake pedal and I loosened the fittings on the master cylinder but I don’t think that did any good. Bled all 4 wheels with Steeles help, The two rear blead OK but the pedal would not go down to the floor, the two front disc brakes bled real good and the pedal went to the floor. Refilled the Master and had steel pump the pedal, I think pumping the pedal did it. Bled all 4 again and WALA!! BRAKE LIGHTS even thought the pedal would not budge for the rears. The rear wheels stop spinning when pedal applied. I think I know what I did to fix it but I’m not sure!!! With front disc and rear drum you must have a compensation valve, does anyone now how to adjust these valves so that 60% is on the front discs?
Dick.
Dick,I used a manual proportioning device on my convert for the rear brakes with disc up front. Used the original Brake T but put a plug in the one orifice I did not need. Sorry the picture is sideways.. [Fixed it! Ed.]
Still have to dial in the Braking ratio after a few hard brakings to see if the front or the rears lock up first.
John Q.
John; Isn’t the verticle master cylinder har to fill?
Yes, it does, But it is a unique sealed systems…errr I guess that would not work either…It would be difficult to fill unless you had a powerfull 413 RB in it that does wheel stands and…and…(ran out of non-sensical things to say for once) 
John Q.
Simply put front wheels on lift and press the button…