91' Suburban with ABS

My 1991 1/2 ton 4X4 Surburban has an ABS brake controller under the hood connected to the master cylinder but no wires or cables going to the rotors or drums that I can see. I did a CAR FAX report on the VIN, it even states "optional" ABS on this particular truck. My father-inlaw was the family mechanic for the owner since it was new. He told me nothing was jerry-rigged or hacked and its pretty obvious to me also, no cut wires anywhere. I plan to upgrade to 3/4 ton running gear when I lift it but I dont know how this first gen ABS works. I would like to utilize it if I can.

Rear wheel ABS only on the '91s.
No wires going anywhere. The control is at the master cylinder.

Rear wheel ABS only on the '91s.
No wires going anywhere. The control is at the master cylinder.
thanx thats what I figured but I was told it cant work like that.