I want to make sure I understand this issue inasmuch as safety is at the heart of it. My '71 F-250 has a dash-mounted light with a red lens just above the foot-actuated parking brake (the word "brake" is inscribed in black letters on the lens). In restoring my truck, I installed a new bulb in the socket and it went on. I released the parking brake, and the light stayed on. It has been my impression for years that the light, located where it is, illuminates to remind the driver to release the parking brake. However, I am told that is NOT the case. The light goes on whenever there is a problem in the brake system as a whole (something about a leak in the hydraulic system and the "proportioning valve"). Is this the case? If so, why in the world did Ford place the light immediately above the parking brake? (Somebody was, ahem, asleep at the switch.) I will value and appreciate your comments/counsel.

 

As I understand this Brake Warning Lamp. It is actuated off of a hydraulic switch. The switch was generally located on the proportioning valve located under the hood on the driver's side inner fender. When the brake fluid gets low or leaks out then that activates the switch, therefore causing the Brake Warning Light to come on. In the wiring schematic, originally there was a green (possibly a ground) wire running from the switch to a terminal on the ignition switch then from the ignition switch over to the light. Then a yellow wire runs out of the light back over to the ignition (most likely hot). Therefore the Light itself should have a green wire and a yellow wire. You may just need a new hydraulic switch to make it go off and operate correctly.

This is how I understand this Brake Warning Light. If you keep a close check on your brake fluid and brake system, you could eliminate the light. Please someone correct me if I am wrong. Hope that helps you out.

 

The switch is mounted on the proportioning valve. When there is a brake system failure or a large brake fluid pressure difference front to rear the plunger in the proportioning valve will move and the dash light goes on.
This is a safety item that should be functioning correctly.
Older drum / drum trucks had the valve / switch mounted inside the left frame rail near the floor board.
It's a pain but when the brake system is fully functional you have to bleed the front and rear to center the plunger in the proportioning valve to get the switch in the off position.

.....=o&o>.....

 

Maybe I should hook mine back up. Beemer Nut, where do you get a new switch and what is the correct name to call it when in the parts store?

 

First we should correct the thread starter on his "parking brake warning light", it is not. It is a brake system failure light.
That switch your looking for is a brake warning lamp switch, to be correct it is mounted to the pressure differential valve on the side in the middle.
The plunger in the valve is centered when the front / rear are equal fluid pressure from the dual chamber master cylinder. This plunger has a skinny center section, if the front or rear brake system has a bad leak or failure the pressure from the working side be it front or rear will push the plunger and the fat section of the plunger will work the switch.
I would be surprised if a parts store had this switch, where is the one on your truck?
If the brake system is all rusty or fluid never changed the plunger will stick and it will become a PITA to center again to turn the warning light off hence burned out or removed lamp but then any failure and you have only the E brake then pray.
Off topic but I have run silicone brake fluid the last 28 years and have not had master, wheel cylinder pitting or this differential valve get stuck.
If the parts store come up empty go to a Pick N Pull for a switch.
I saw your gallery, hey these trucks need a FE under the hood, sorry.
.....=o&o>.....

 

Yes, try a junk yard, we stole the proportioning valve of the '78 when we stole the front axel and it had a switch in great shape - only I didn't know what it was for - now I do!

Peter

 

The word is liberated, chebbie owner use stolen parks to keep their wrecks running.
.....o&o>......

 

Hey Beemer Nut,

My truck did not have one of those switches when I bought it. It was pretty much a mess when I got it. It has taken me five years to get it restored. I am still working on small things. I will most certainly try to find one of those switches and get'r working properly. As far as a FE under the hood, I agree except my truck came with a 240 I-6 and I wanted a V-8. I found that 351W for $200. It's not an FE, but at least I got my V-8 now.

 

Just poken at ya with a 351 W, I see that's a big upgrade vs a six.
That W motor has a lot to offer if you decide later to build a stroker and a lot cheaper than building a FE.
Now a 351W stroked and in a 48 F1 would be great, oops wrong dream.

On the brakes I see a trip to the wreckers in you future as there a lot of brake parts available. Hope you get everything squared away.

.....=o&o>.....

 

If I were to upgrade to front disc brakes in the future, will the same switch still work in that application?

 

Someone asked for an illustration.

Here you go !

Unfortunately the whole pic didn;t scan.

The arrow at the top pointing right is pointing to the Brake Failure plunger device which when pushed up from the un-even pressure turns the light on.

 

my warning light is on too..i have bled the brakes and light will not go off. the brakes do feel fine and i have no leaks anywhere. could the switch be the problem?

 

It just need equalizing.

Some times it takes 2 people to do the bleed and reset the switch.

Have you tried pressing REALLY hard on the pedal to reset it ?

 

As Mil1on said it takes two people and then if your lucky you will get the plunger to move side to side past the center off position. Many times with these units this old it is just stuck.

.....=o&o>.....

 

I gave up on the "recentering" thing. The truck stops fine. No leaks, nice dual skid marks on the street. I unplug the light for state safety inspection.