Black box behind glove box, what is it?
 

I need some help. I just bought a 93 1 ton dually 4x4 auto. I was tracking down a vacuum leak that was driving me nuts and I dropped the glove box to get up under the dash.

There is a black box with a large grey plug with probably twenty wires coming out of it. The plug is disconnected. WHAT IS THIS BOX?

If anyone knows, please let me know. I was going to plug it in and see what happens but figured I better see what it does, maybe there was a good reason someone disconnected it.

That's the computer for the rear wheel anti lock brakes. It was probably disconnected to mask a problem with the RWAL system. Dollars to donuts you plug it in and the light stays on.

Can it be fixed like that later models by replacing the WSS?

If you plugged it back in, you'd have your BRAKE and ANTILOCK lights come on in the message center, and your rear wheels would lock up under normal stopping conditions.

Why would the rear wheels lock up under normal stopping conditions? My light is on and they have never locked up, except on ice.

You can have BRAKE and or ANTILOCK lights on for various reasons. When you have a problem in the RWAL system, you're rear brakes can lock up under normal stopping conditions, let alone hard braking on dry on pavement.

If you disconect the "Black Box" for the anti lock brakes, the rear brakes will function the same as the older trucks that never had anti lock brakes. I removed the black box and valve from mine when I did the conversion ( my diff does not have a speed sensor in it) and the brake function is not any different than before.