When I replaced one of my electrical switches, I killed all of the electrical power to the trailer. I.E., un-plugged the 50AMP power cord from the pedestal and removed the 12V positive cable from the battery. I also checked that the wall circuit with a multimeter just to be sure, you can never be too careful.
I than replaced the light switch that had failed.
Now when trouble shooting an electrical system, this can be done with the power on. I would remove the wall plate and check to see if power is at the circuit. A multimeter or several different circuit testers that are available for either 12V or 120V systems can be purchased and used. The circuit tester will indicate that there is power to the receptacle/switch or not. If there is no power to the switch/receptacle than look at a fuse in the fuse panel or circuit breaker to see if the fuse has failed or the circuit breaker has trip.
Replace the failed fuse or reset the circuit breaker. If the fuse immediately fails again or the circuit breaker trips immediately. Then a short or overload condition is present and needs to be fixed.
2016 34RL CC; 2008 Ram Mega Cab 2500HD, 6.7L, 68RFE 6 speed, 4X4, Smarty S67, TDR 145K+miles