I am no expert, but here are a few things I would try.
- Disconnect the wire from the 12 Volt receptacle where you plugged in the cooler.
- Does the red light on your converter box stay on, if yes turn of and then back on shore power and battery power (let it reset in other words)
- If your lights are all led, make sure you have at least 12 Volt going through the fuse, led's have a narrow operating range.
If you have, lets say a 10' 16 awg wire going from the fuse panel to the receptacle in question protected by a 30 Amp fuse the whole wire might have started to melt before the fuse went.
I'm just guessing