bilge pump fishfinder,live wells and horn doesn't work

On my crestliner I have a accsory switch which runs my live wells,radio and fishfinder. I also have a switch for a bilge pump. Sometimes everything turns on fine and most times nothing will turn on at all. Where do i start to look for the problem. also the horn is the same. somtimes it works moost times no. thanks for your help.

corey