The rear anti-lock light on my dash is on. I was thinking it was the speed sensor in the hog head. Does anyone know what else it could be? Would like to diagnose everything at once.

 

I would check the wiring in the sensor in the rear end. As these trucks get older it will start to come loose sometimes. I would disconnect that sensor (after the negative battery cable) and clean and inspect it. Then reconnect it and the battery cable and see what happens.