My abs light came on last week. I was told that it could be my speed sensor on the rear end, so i changed it. Light is still on. But i just noticed this. If you hold your foot on the brake and start the truck the light won't come on. You can drive the truck with your foot on the brake still no light. But as soon as you take your foot off the brake the light pops on. All the fuses are good, its full of fluid. Does anybody have a clue whats causing this? I know theres a pressure switch on the brake booster could that be the problem? And would that make my transmission shift weird? Sorry for the long post. Thanks,

 

Have it checked at your local ford dealer, most shops can not access the ABS codes and cycle the ABS valve and controller.