Hi all,
new to the forum and as I e read I can see this is a great tool for those of us new to the first gen world. I have both my antilock brake and parking brake lights illuminated on my 1992 w250. The service manual says there are fault codes that will help you diagnose your RAWL problems but it asks you to “ground the RAWL diagnostic connector”. How does one do that?

Thanks!
Ray

 

Good question. I haven't been able to figure that one out either.
I replaced the hall effect sensor on top of the rear diff, didn't solve it.
Someone once told me the controller has a vacuum line to it and if the vacuum is slow coming up it will set a check light. Haven't been able to confirm that either.
I have an FSM and still can't sort it.

 

i found it. Behind the glove box there’s a ABS control module. The wiring harness has a black wire coming out of it. At the end of the wire is a connector with 1pin in it. That’s what you use to ground the module.

 

No vacuum lines associated with the ABS. The system is simple, only 3 main components. The sensor, the control box, and the valve. The most common failure is the sensor. Still available the last time I checked and easy to replace. However the wiring harness to it is susceptible to moisture intrusion which really messes with the signal to the control box. The valve rarely fails electrically, but it is susceptible to internal corrosion leaving you with spongy brakes. These are no longer available. I don't recall hearing of a control box failure. I finally gave up on mine and bypassed the valve.

 

I bought an adjustable proportioning valve because I swapped to Eldorado disc brakes in the back a few years ago. I intend to put it in and remove the dump valve at some point. I will just remove the ABS bulb.

 

Not ABS, but there is a vacuum switch that will trip on low vacuum and turn on the brake light in the dash. Most (if not all) of my cummins trucks have this.

 

Oooooh that makes so much miss sense! Thanks for the clarification.