The built in trailer brake on my truck is not working.
Hello. If the trailer brake system is not working, then it may be a blown fuse or it can be a trailer plug problem. This truck has a history of the terminals in the plug breaking and causing similar issues. As a mechanic, I would check the fuse first for the trailer brake. If it is blown, then it should be replaced and checked to see if it happens again when the trailer is hooked up. If it is, then the trailer is causing the fuse to blow. The best way to diagnose this further is with a voltage meter to see if there are intermittent connections at the trailer plug. If you need further assistance, I recommend you have a mechanic, like one from YourMechanic, inspect the electrical components and repair any damaged parts.