How to troubleshoot a trailer ABS light on a truck?

When a trailer ABS light is on, don't immediately blame the control module. Often, the problem lies in the plugs, wiring harness, wheel speed sensor gaps, or mud/water ingress in the connectors. I once encountered a truck that would trigger an ABS fault as soon as the trailer was connected. The driver thought the trailer was broken, but it turned out the seven-way plug was oxidized, causing a…