Look at the rubber brake flex hose going to either front brake. The front hubs for four wheel ABS have a wheel speed sensor, and its wire harness is smaller in diameter than the hose, and is clipped to it. The two run parallel to each other, and about an inch apart. Follow the two steel brake lines from the master cylinder, and you will see them go into a fairly large hydraulic controller with another three or four lines coming out of it. That controller will have a lot of wires plugged into it.
If you have rear-wheel-ABS, (RWAL), there will be no wheel speed sensors or wiring at the front wheels. Most models have only a single sensor on top of the rear axle's center section. The two steel lines leaving the master cylinder go straight down to a small brass valve assembly, (about four inches long and one inch wide), bolted to the frame. Three lines leave that block. Two go to the two front brakes. The third one, on the rear, goes to a dump valve assembly bolted to the frame rail, close to right under the driver's feet. A single line leaves that to go to the rear axle.
Trucks usually also have a sticker in the glove box listing the optional equipment.
The bearing assemblies are the same for both applications. If you use a four wheel ABS bearing on a vehicle with rear-wheel-ABS, just do not connect the wire. Wind it up and tie it out of the way.
Monday, April 10th, 2017 AT 4:12 PM