ABS on your 89 is not self-diagnostic so you can't retreive codes. That didn't happen until midway through 93 models year on 900 series (never happened on 240's).

ABS faults fall under three categories:

1. light is on and remains on after engine start- no power to abs ecu, wiring faults, no power to abs pump/modulator assy.

2. light goes out on eng start but comes on after the self-test at 3-7 mph-

pump motor or pump motor relay fault, open wheel speed sensor circuit, or lack of signal from sensor

3. light comes on after a distance and at speed- position-dependent opens in sensor wiring (broken wire in cables to wheel sensors that shows up on bumps), erratic signals from sensors, interference in signals from sensors (wheel speed sensor wires too close to plug or coil wires,etc.), damage to pulse generator "gears" on hubs or in diff.