To find out if a vehicle that was built before 1998 has an Anti-Lock Braking System (ABS), you can:

Question

If you are operating a vehicle built before 1998 and are unsure if the trailer has an Anti-Lock Braking System (ABS), you can check under the trailer for wheel speed sensors coming from the back of the brakes.

Accepted Answer

Check for wheel speed sensors coming from the back of the brakes.

Answer

Pump the air brakes to activate the ABS.

Answer

Look into the back of the fifth wheel.