First off the Brake light and ABS light come on and stay on until I turn the engine off. they may come on the first time I apply the brakes or it may do it the 10th time I apply the brakes. They always go on together. Never one or the other. Once they go on they stay on until I turn off the engine.
Now the weird part. As long as the brake and ABS lights are off the brake pedal responds normally. I push the brake pedal about a 1/3 of the way and it brakes smoothly.
But when the lights are on, the brake pedal contact point is much higher. I only have to push the brake pedal about a 1/4 inch before it engages. The brakes appear to respond OK.
This happened shortly after (6 weeks or so) after I installed new rear brake pads and had the drums turned and brake cylinders replaced. (not sure it had anything to do with it)
I'm stumped except to think it may be due to a proportioning valve sticking or something... probably a bad guess. I plan to replace the brake fluid to see if this helps since it probably needs it anyway. All the fluid levels are OK and there are no visible leaks.
the truck has 130K miles and is the most trouble free vehicle I've ever owned.
I had the same thing happen to my '88 Chevy. At low speeds, no problem, but when she had a head of steam up, I'd hit the brakes and it would sink and the brake light (it has rear abs, but there is only one brake light) would come on. I could physically feel that the truck was NOT stopping right. This led to me pumping like a madman every time I saw a possible stop ahead. Turns out the retards who did the work on the rear brakes put the auto adjust finger back on wrong (I've gotta stay and watch these people from now on or do it myself). This caused the rear brakes not to be able to fully engage. All I had to do to fix it was simply set the fingers back thbe right way. Unfortunately, I figured that out after I bought a new master cylinder .
It could also be air in the line or a bad master or wheel cylinder, but I doubt it's a bad cylinder since the levels are ok.
I wouldn't think you'd even find it a problem on a Ford. My '82 Ford only has front brakes and it stops better than my '88 Chevy with brakes all around.
This is way off topic, but i've noticed too that Ford has way smarter people designing their brakes than chevy does. Kudos to Ford for making brakes that stop faster and smoother than chevy (at least on older trucks).