To troubleshoot the electric system of an RV, check if the coach battery of an RV is charged. To do that, remove all the external electrical sources, turn on an electric appliance in the cabin, and inspect the dashboard on the RV. It may indicate that the battery is low.
The more complicated way to check the battery is by using a multimeter. Set the device to 12-volt DC, connect the probes to respective terminals. The battery is in a good condition if the multimeter indicates a value from 12.6 to 12.7 volts. If the value is lower than 12, charge the battery.
If that didn't solve the problem, make sure that the battery disconnect switches are on. Inspect all the devices in the cabin, and determine if all of them aren't working or just some of them. Find the power distribution center of an RV, and locate the fuses for the appliances that aren't working. Make sure that the grounding is safe, and check both sides of the fuse using a 12-volt test light. If only one of the sides is working, install a new fuse.
If the appliances are still not functioning, test the device switch using a test light. If the switch indicates a value of 12 volts, find an inline fuse in the wiring of the appliance. Test wires on both sides of the inline fuse, and install a new fuse if there is a problem.