When I noticed that the brake light was only going on when I pressed hard on the pedal I obviously replaced the switch. However, it still does the same thing with either switch. I can back out of the driveway or come to a "reasonable" stop on the road and never turn the brake light on. I can always press harder and make it come on. According some brand manual I have for F150 and Broco for that year I need to bend the bracket, but there is no bracket to bend. Another website says the switch deactivates when the brake is pressed. That is wrong too. This is normally open and both test correctly when the pluger is depressed. I even saw a post where someone installed it upside down and it worked, but the tabs on mine won't let it fit upside down.

If the engine is off (no vacuum boost) peddle travel of about 1/2 inch turns the light on. With engine running (with vacuum boost) I need about 2" of pedel travel.

I'm an engineer and this one has me stumped. I have considered putting a spacer between the switch and brake rod end or even removing the round plastic bushing allowing more play in the hole/pin setup. But this can't be "right". I noticed a dimple in the end of the switch bracket. Is that there for a reason, have I lost an important piece... like a spacer? My assembly goes like this:
On the round rod from the pedal I have a white plastic washer, a black shoulder bushing, the switch and push rod , a 2nd white plastic washer, and the spring/cotter type key. There is nothing between the push rod end and the switch pad. Help!

 

The switch should make and turn on the brake lights before the rod to the vacuum booster starts to move.
Make sure the wires are dressed right or the lights will stay on or not work right.
Pushing harder should have no effect.
You should be able to move the brake arm back and forth by hand and hear the switch click.

/

 

Thanks subford for the diagram. Now I know I'm not missing anything. That picture is exactly what I have and how it is assembled with the exception of a 2nd washer (#4) between the switch and pedal (#6) which goes on the shaft first.... seems there should be one there since the metal plunger plate tabs from the switch which push the spring down would bind on the pedal without one. I just tried removing the clip to prove it wasn't binding somehow and even floating on the shaft it sill only works when I press harder. The wiring connector only goes on one way with locking tab and mine has wires exiting from the top instead of the rear as shown, but that harldy seems to make a difference. There is slack in the wires and nothing is getting caught during movement.

Yes, I can move the pedal with truck off and faintly hear the switch. Push the pedal aprox 1/2" till it meets the 1st resistance and the light turns on.

I know this sounds crazy, but is it possible the swtich is fine but the vacuum boost is too sensative or the spring that returns the arm is weak? Doesn't feel week when engine is off though.

 

I have the exact same problem on my '92 F-350. I have played with it off and on for the last year and half. There are no missing parts on mine, I have also changed the switch as well. Still works the same.

 

My 89 F150 brake lights also don't come on when it should, isn't bad enough to bother with, but still, sitting stoped, I can release pressure, but not enough that truck moves and the lights turn off.

 

I have the same problem on my 2000 f150. Brake lights work, but if you, very slightly, let off the pedal, the lights go out. This would not normally bother me, but I just got a new trailer with electric brakes, and the brake controller applies trailer brakes when the truck brake lights are on. When I roll up to a stop light, the trailer brakes are on, off, on, off,on, off. It makes for a very jerky stop. I've narrowed it down to a flaw in Ford's design. The brake push rod does not return fast enough with the pedal. I was thinking about drilling a small hole in the push rod, and hooking a spring to the brake pedal and through the hole in the push rod making them essentially one piece. The only question is, would the brake lights go out when the pedal is in the full up position? Any help would be greatly appreciated!

 

I ended up drilling the hole in the push rod, and not connecting the spring to the brake pedal, but to the under-dash frame, so it pulls the rod toward the driver at all times. Seems to have totally fixed the intermittent brake light problem. The brake lights are on unless the pedal is in the full "up" position no matter what you do.

 

Ok I know this may not help but this was what happened with my truck (which I thought was odd but it was similar to this I think, but here goes...this may not help but it could give another idea...

when my truck lights didnt work correctly I too thought, switch and wires and that mess, well I checked the parts they were fine so I just on the off hand figured what the heck, check the lights, so I looked and my bulbs were 3056 not the 3157 as they should be, granted they are LEDs I have but my driver side would act as if the breaks were pressed and the passwenger side would only flash (till it shorted out) no stop light, so I swapped out the bulbs and all is working well...

don't think this will be what your experiencing but figured id throw it out just incase as this is what i experienced...