The Anti-lock Braking System (ABS) relies on wheel speed sensors. If the ABS light is on, the wiring diagram shows the pin numbers at the ABS ECU and the exact wire colors for each wheel sensor. This allows you to test resistance at the ECU connector rather than crawling under the truck to each wheel individually during the initial diagnosis.
Now, test voltage at each highlighted point sequentially. When the voltage drops to zero, you have found the break. isuzu frr 500 wiring diagram