The typical RV will be equipped with a 30-amp RV distribution panel that has 120 volts coming into the unit. Power comes in into the RV distribution panel via the power cord or “shoreline” cord from an outside electrical supply or onboard generator. The 120-volt AC appliances are protected by residential style circuit breakers. The 12-volt DC operation is protected by automotive style fuses and provide power for the roof vents, lights, water pump, and appliance operating on the LP mode.
Fuses are not like breakers, meaning once they blow they have to be replaced. There is no resetting fuses on an RV distribution panel. If a fuse is bad it will appear burnt a little on the inside of it. However, you can test for a bad fuse to verify that is the problem. Place a 12-volt meter at the bare metal section on the top of the fuse. If it is not lighting up, it is a bad fuse. Newer RV distribution panel models will have lights underneath the fuses and if the light is on, it is indicating the fuse has gone bad.
When working with an RV distribution panel make sure that all power coming into the panel is disconnected and you are wearing the proper safety goggles. The only time power should be on when working on the panel is to test and read power levels. When reading power levels of fuses, verify each one has 12 volts of current.
Knowing how the distribution panel is set up and how to determine if there is a bad fuse, will help you troubleshoot most of your electrical system issues.