I just bought a 1990 F-350 4x4 and the rear anti-lock brake warning light on the dash is lit up. I don't have an owners manual to refer to. Does anyone know why this might be on? Thanks, Missy

 

check to see if the brake fluid is up to max in the master cylinder. also check the inside of the rear wheels to see if they are wet with brake fluid. if so you may have a leaking wheel cylinder that needs to be replaced. let me know what you find. james

 

It also may be the rear wheel speed sensor. These are known for failing. It is licated on top of the rear end housing. Click here. This page is for removal and replacement of the rear wheel sensor. Click here for a page to diagnose the ABS system.