Wash the rotors? Not sure what that will accomplish but make sure you wait until the rotors are cool before you wet them.

ABS doesn't pulse the brakes in a way you'll feel pulsing. It feels more like rollerskating on a pebble wash surface. If you feel the brake pedal pulsing in a way that pushes back against your foot, that's probably warped rotors as mentioned above. Sometimes warped rotors also cause steering wheel shimmy when you apply the brakes.

If I'm not mistaken, the ABS light comes on when the ABS is engaged. Not really sure of this. If you're daring, cut power to the ABS and see if the pulsing continues.

Sixto
95 S420
87 300SDL