Troubleshooting electrical problems on travel trailers and vehicles is extremely challenging. The difficultly is that most of the wires are hidden inside the metal frame tubes or wall systems. Luckily, electrical connections must be made accessible for inspection and repair. Narrowing down the faulty connection in a trailer electrical system is a job of trial and error. A wiring diagram, supplied by the manufacture, is the best method for determining the path of each conductor.
Determine which portions of the trailer's electrical systems are having problems by testing each device for operation.
Confirm there is no power at the connection from the device to the trailer's electrical with a test light. A test light works by connecting its alligator clip to a common grounding point and touching its probe to the bare metal of the hot wire. If it illuminates, there is power at the connection and the device itself maybe faulty.
Follow the wire along its path as far as you can checking any point of connection with the test light. If you find power on one side of the connection, but not the other, make repairs as necessary.
Refer to the wiring diagram for the travel trailer if the conductors disappear into walls or the metal framework. The diagram will show the location of the next connection in its path. Check each connection with the test light working your way back to the distribution panel.
Check the fuse panel in the trailer for blown or tripped breakers. Each circuit is labeled for its purpose on the inside of the panel's door.