66 brake lights

[Major Tom]

I no longer have brake lights on my 66 roadster. Several years ago I converted over to a dual reservoir master cylinder,but I plumbed in the 66 brake switch. this has worked fine for years but now they no longer work, I do have lights, blinkers and flashers. I know that on the 2 wires going to the switch one has constant power and the other gets power when you step on the brake pedal. My question is what completes the circuit when you step on the pedal ? is there a contact of some sort on the pedal ? Keep in mind this a 1966. I have replaced the switch , but have no power to the second wire

 

[B RON CO]

Hi, the fitting is the brake light switch. The hydraulic pressure closes the switch when you step on the pedal. As you know, one green wire is always hot. If one is not hot you have to figure out why. I'm not sure if there is a fuse.
There are two test you can do next. Pull the terminals off the brake light switch just enough to expose the brass post so you can touch them with your test light. Have a helper steps on the brake pedal and both sides should be hot.
Next you can also pull the wires off the switch and jump them together with a piece of wire and the brake lights should go on
You probably have to just replace the old switch. You shouldn't have to bleed the brakes, just quickly undo the old switch and put in the new one.
Good luck

 

[EPB72]

If you jump the wires at the switch do you have brake lights?? if not wiring between switch nd lights which does go through the turn signal switch ,,or if lights work when jumped then the switch is a issue not uncommon to be bad NEW "never ever works"

 

[Major Tom]

Hi, the fitting is the brake light switch. The hydraulic pressure closes the switch when you step on the pedal. As you know, one green wire is always hot. If one is not hot you have to figure out why. I'm not sure if there is a fuse.
There are two test you can do next. Pull the terminals off the brake light switch just enough to expose the brass post so you can touch them with your test light. Have a helper steps on the brake pedal and both sides should be hot.
Next you can also pull the wires off the switch and jump them together with a piece of wire and the brake lights should go on
You probably have to just replace the old switch. You shouldn't have to bleed the brakes, just quickly undo the old switch and put in the new one.
Good luck

You mentioned that hydraulic pressure closes the switch. this has got me wondering. When I checked the brake fluid level the smaller reservoir was low, not empty but very low. I did jump the wires and got brake lights. I think I am going to bleed the brakes and see what I get. Thanks

 

[Broncobowsher]

The low reservoir is either a leak or the brakes are not self adjusting. Exception is if you have disk brakes, that will lower the level in the master as the pads wear.

Fastest and simplist check is to unplug the brake switch and jump the two wires. If the brake lights are on, bad switch. Yes, they do go bad.

 

[B RON CO]

Hi, if the brake fluid is low I would check all the wheel cylinders for seepage, rust and anything that could be bad. It is very important that the brakes are in perfect working order. It is common to find frozen and leaking wheel cylinders. Not a small job, but for piece of mind, if you haven't done that in a few years. Check all the brakes and grease the front wheel bearings. Good luck

 

[SteveL]

The smaller reservoir should go to the rear brakes. Check and see if you have a wheel cylinder leaking. If you have a leak maybe theres not enough pressure to activate the switch.

 

[Major Tom]

The switch is new. I have checked and don't see any signs of leakage. I will check again when I bleed the brakes.
Thanks to everyone for their help.

 

[mrdrnac]

Your brake light switch is plumbed to the larger reservoir, so the front (smaller reservoir) being low would not affect it. Since you jumped it and it turned on the brake lights, your new pressure switch is "Bad". Have you tried standing hard on the brakes to see if it works then? Sometimes these pressure switches take a lot of pressure to work. That is why I fabricated a mechanical brake light switch to work off of my brake pedal for my 66.

 

[Major Tom]

Your brake light switch is plumbed to the larger reservoir, so the front (smaller reservoir) being low would not affect it. Since you jumped it and it turned on the brake lights, your new pressure switch is "Bad". Have you tried standing hard on the brakes to see if it works then? Sometimes these pressure switches take a lot of pressure to work. That is why I fabricated a mechanical brake light switch to work off of my brake pedal for my 66.

thanks, I will take it for a short trip around the neighborhood and see what I get

 

[Major Tom]

PROBLEM SOLVED.] took it for a short trip and stood hard on the brakes. the brake lights now work. I don't think the new switch had enough pressure in it yet .
I am still going to bleed the brakes and check for leaks.
Thanks to everyone for their help, you guys know everything

 

[mrdrnac]

Glad it helped. However, I think the Hydraulic switch just requires a very firm pressure on the pedal to work the brake lights. I think safety reasons are why the manufacturers went to the mechanical switches, because even very light pressure on the brake pedal will actuate them, so even if you are just riding the brake pedal the brake lights will light. This gives the car behind you more notice of your braking.

My Wilwood brake adjuster had the hydraulic switch on it, but it always takes too much pressure on the brakes to light the brake lights, so I added another circuit to work the brake lights mechanically as well, sort of a back up system.