I noticed that the old owner of my truck painted over the rear antilock dummy light. My truck slows fine, any clue why the light would be on? 1989 F250 4.9

 

Check the master cylinder. As the pads wear down the fluid level drops, if it gets low enough the light will come on.

There is a sensor on the pumpkin of your rear axle. Sometimes it gets covered in metal shavings and no longer gets the correct signal. You might pop it off and clean it.

Mine was on too when I first got my 87. There's a connector under your dash that you can jumper and the light will flash a code. Mine said that the solenoid in the module wasn't actuating.

Then I replaced the front breaks, calipers, hoses and pads, bled the front part of the tank dry and filled with fresh fluid. Power bled them, never even touched the rear circuit. I guess I also added a few extra ground straps off the batteries. After about a mile the light went out and hasn't come back since.

I think the moral of the story is with old trucks sometimes it's best to just start doing any routine maintenance that might have been overlooked, then start on the diagnostic work.

The RABS is done with a little module on the drivers side frame rail. It has a bleed screw, you might grab a bleed bottle and some penetrating oil and try to flush it out.

I think the proper bleed order is rear drums, and then the module. I've never touched mine.

 

They weren't the most reliable system out there...

 

The light is on in My '87 F250 I just got yesterday, has rock solid pedal and stops on a dime