Every rig comes with a fuse panel, but not all of them are adequately marked. Lighting circuits can be oh, so clearly marked: "Lighting 1,""Lighting 2," etcetera. If you do blow a fuse then it's a matter of not knowing which circuit is which, and pulling fuses until you get the right one. In some rigs it's even worse: Fuses without identification. Here's a simple identification assignment: Shut off all your 12 volt users, lights, water pump, et al. Now pull out a single fuse and see which appliances don't work. Label the fuse appropriately and repeat until you know which fuse operates what. Keeping a batch spare fuses close (or inside) the fuse box really helps.