ABS Light

Is it the Trailer Back warning light staying on or the Dash warning light, try to Isolate as the Trailer has it's own ABS computer. Like someone else said try driving in the yard, you need to go 10 mph+ for some distance to reset the computers. Next if it's safe in the yard try unplugging the 7 pin power cable to the trailer and do the rolling test again to see if the Tractor dash light goes out.

If the dash warning light goes out, then the problem's in the Trailer,,, If it stays on, it's in the Tractor. What I've seen in cold weather is moisture gets into the Aluminum sensor mount and Freezes, cracking apart dropping the wheel speed sensor loose in the Brake assembly, breaking it's wires.

If it's the tractor, you could pull the tractor's ABS fuse to dissable the dash light, first problem is when you start the engine is the truck goes thru a self test,, if everything is working properly then the trailer warning light will come on during the self test then go Out,, as will the tractor dash come on the go out. Second Problem is a smart DOT inspector will know this also and know if the ABS system has been dissabled $$$

I'm not advocating dissabling the ABS warning system as that's against the LAW,,, Just trying to help you understand how I would trouble shoot the problem,,, yes I do have a Brake Inspector Card,,, Dan

Thanks it's the trailer