My mother has a camper and needs to run wire from where the AC is. She tells me that the wire that is there now is for an air conditioner and she needs to down size the wire to a 12 volt wire. Problem is we have no idea how to do this. I told her I believe that if the wire in place now holds so many volts it will remain that way regardless if she runs smaller wire and possibly burning up the new wire causing problems. She said that she has a power box and a converter box also. She said that there are fuses so my next question is this. Can't she find out which fuse is connected to the line then switch fuse size to match the line size? I have no clue. Please help.

I am not familiar with any campers, my idea of camping is a Raddison, Holiday Inn, etc.

If the AC needs 12 volts, which is DC from the camper, the line voltage from a building is 120/240 AC volts. Really need more info on the "converter box" you have.

Something is needed to reduce the AC line voltage down to the 12 volts DC. Simply replacing a fuse or running smaller wire is not the answer.

May I suggest trying to ask this question over at Cars & trucks, this would be the closest you could get to a camper. Perhaps someone there may be more familiar with the power converters in a camper.