Potential fire hazard.
The original brake light switches held up pretty well, but when they go the replacements are less than perfect. I've had a number of them leak right out of the box.
I don't know why they didn't use a power relay that would power down the brake lights when the ignition is off. Why would you need brake lights if the car is not powered up with the key? I can see why you wouldn't want the headlight circuit on the key, but why not the brake lights? There are no 4-way flashers, so what's the point?
Do you recall the rash of fires under the hood of Ford pick-ups a few years ago? Just like the design of our switches flammable hydraulic fluid gets past the rubber diaphragm and enters the chamber that houses the electrical contacts. The housing is grounded to the car body through bolting on the Treadle-Vac. With 12-volts present all the time a real danger lurks inside the switch. Just a slight arc is all that's needed to set hydraulic oil ablaze.
This was happening on newer Fords that had cruise control. Instead of turning on the brake lights it's used to open a set of contacts that disconnects the cruise control when you hit the brakes. The same conditions exist in our brake light switches. Constant power, flammable fluid on the other side of the switch and an 18-amp fuse on the headlamp switch. It would take far less than 18 amps to start a fire.
My friend's '57 would present him with a dead battery on a frequently increasing basis. One day the went out into his garage and found his brake lights on. He'd get in the car and push on the pedal a few times and the lights would go off. Finally, the battery wouldn't last the night. Not knowing, he replaced the battery and it was dead the next morning. That's when I got the call. He jump-started it and he made it to my shop. Disconnecting one of the switch leads made the lights go out. The switch was hot to the touch, much hotter than similar things not attached to the engine. I cut it in two, and, sure enough he was "this close" to burning up his car, and his house.
Ford went to a mechanical switch on the brake pedal, but left the hydraulic switch on the newer cruise control. I'm trying to devise a way to use a mechanical switch while leaving the hydraulic unit in place, but unpowered. Has anyone done this? In the interim I'm looking at using a battery disconnect on every vehicle vehicle I have that uses a hydraulic switch as it has the same inherent risk as the later Ford products, constant power and flammable hydraulic fluid. While the only evidence I have is anecdotal, it should not be ignored.
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