Newbie here with a RABS problem. The truck is a 1991 F-150. While braking, the rear brakes lock up and stay locked. Electrical troubleshooting is not my strong suit. But the red "brake" light does not light up when the key is turned on. It does work when the emergency brake is applied. I think I have traced that down to the diode resistor. Of course, the dealer does not have this in stock.

The yellow "anti lock" light illuminates when the key is turned, goes out for a couple of seconds, then stays on. My current problem is, I can not get the RABS to give me a code. My Chilton book tells me to disconnect the "diagnostic connector" located under the dash. I can't find it. There is a pig tail with black/orange wire that I tried, but it did not work. How do I retrieve the codes?

I thought I could just disable the RABS unit and limp it around town while my part is on order. So I disconnected the control module, but as soon as I stepped on the brake, the rear brakes locked up and stayed locked. Is it possible there is another problem such as the proportioning valve?

Any help/thoughts will be appreciated. Thanks.

Mark

 

The problem has been identified and fixed. It turns out the flexible brake hose that runs from frame mounted brake line to the brake lines on the rear end (goes to a T connector) had deteriorated internally. This debris acted like a one way valve. Fluid pressure could go to the rear brakes, but could not flow backwards when the brakes were released.

Brake hose failure is somewhat common on front brakes, but rare on rear brakes.