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Barry Wolk
09-09-2024, 07:02 AM
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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Llfordman
09-09-2024, 08:48 AM
Why not use the hydraulic switch to pull one side of a relay coil to ground? Current is probably around 150ma to do this. The hydraulic switch should live a pretty comfortable life in this mode.
Battery cutoff switch is a great idea also.

Barry Wolk
09-09-2024, 09:01 AM
I don't believe that will solve the problem because current is still available. While the bulbs are no longer the load that doesn't preclude a fire as an arc to ground is as likely as an arc from contact to contact.

I'm investigating two locations for 300-amp disconnects, under the battery, and inside the fuse box with the handle under the box. My car is not here for me to test that, but I'm pretty sure it would be pretty accessible there. There's plenty of room for it inside the box.

Joseph Stebbins
09-18-2024, 10:13 AM
What about a simple high amp solenoid that engages when the ignition is on or has a simple toggle switch hidden (like you hide an electric fuel pump switch). It would fit in the fuse panel box pretty well

https://www.sonicelectronix.com/item-46583-NVX-BIR500.html?utm_source=google&utm_medium=cpc&utm_campaign=PLA&utm_source=google&utm_medium=cpc&utm_campaignid=21712131812&utm_matchtype=&utm_keyword=&utm_device=c&utm_content=&utm_devicemodel=&utm_network=x&utm_loc_physical_ms=1018036&utm_loc_interest_ms=&utm_placement=&utm_adposition=&gad_source=1&gclid=Cj0KCQjw9Km3BhDjARIsAGUb4nzfM7HfXlx2GL2evsSa 73XkUmYsniR_89W2mXC9wLr-_r5qbtDHgNcaAlg5EALw_wcB

Mark Norris
09-23-2024, 03:12 PM
Yes, that's what I fitted. Switch is under the driver's side dash (next to the electric top up fuel pump) and the solenoid is hidden under the battery tray. I don't trust 70 year old wiring especially since a lot of the circuits are live even with the ignition off.