Do not upsize the fuse. Fuse size protects the wire. A larger fuse can let a small short become a melted harness.
Start by naming the circuit
Use the panel label, but do not trust it blindly. RV labels are often vague. Turn off or unplug everything on that circuit: lights, fan, pump, furnace board, USB ports, tank heaters, radio, slide controller or awning controls.
Replace once, then isolate
- Install the exact same fuse rating one time.
- If it blows immediately, leave the fuse out.
- Disconnect the easiest loads on that branch one at a time.
- Inspect recent work areas first: screws through walls, new accessories, battery changes, water leaks and rodent damage.
- Look for wires pinched behind lights, under slides, near metal frames or inside exterior compartments.
When the fuse blows only during use
If it blows when the water pump starts, the motor may be drawing too much current or the wiring may be rubbed through where the pump vibrates. If it blows when a light switch is flipped, remove bulbs or LED fixtures from the circuit and inspect polarity and connectors.
Use smell and heat as clues
Warm plastic, a hot fuse, or a burned smell near a fixture tells you to stop. Do not keep feeding the circuit while searching.