I just went out and took a good look (by flashlight) and it looks like the brake light switch rides along with the pedal lever, right where it connects to the booster rod. I guess it depends on a little bit of slack in the booster rod linkage to actuate. I hope you understand what I am saying. The switch is not hardmounted to the dash, it rides along with the brake pedal lever, all the way to the floor. The booster rod linkage has I guess an oval hole in the brake pedal lever, and it depends on the pedal to move forward before the booster rod is pushed forward.
The lever should move forward, and activate the switch, THEN start to push the booster rod forward. I guess I have a sticky switch which is riding along with the pedal lever until I add the "pushback" pressure of the booster.
I guess I need a new switch. I will try the F350 switch idea, and update the thread.
OK, so time for an update. I went to my friendly pull-n-save junkyard and grabbed a brakelight switch from an F150 and from an f350. The f350 switch is sprung much lighter, just like you guys said.
first I put on the f150 switch, which is identical to the bronco switch (no big surprise there). but the brake lights still acted like before, I have to press the pedal a little harder than "stopped at a light" to get the brake lights to light.
I pulled the little black plastic busing off of the brake pedal pin to give it a little more play before the pedal started pushing the booster rod forward. This made a big difference, but still not as fast of a reaction as I wanted (have to push the pedal about 1" before the lights come on, but lights are on before the brakes start grabbing.)
Then I put the f350 switch on with the bushing. Same results as before, I have to press harder than "stopped at a light" to get brake lights. tried the f350 switch without the bushing, and voila! If I press the brake pedal about 1/4" I get brakelights. the lights stay on until I take my foot off the pedal, and I don't get any "false" brakelights over bumps or traintracks.
So here is my question. what gives? Is my brake booster/master cylinder getting so easy to push in that it is unable to trigger the brake lights when the bushing is installed? If so, which do I need, a booster or a m. cylinder? It is like the brake system is too compliant to the pedal input to trigger the switch.