blown fuse #1

i have a 98 mercury grand marquis 4.6 keeps blowing fuse #1 i start by explaining was happening first off . if radio is on or off aftermarket radio /cd player , i can hear static coming from the rear speakers. with ignition.switch to run position. radio would not play just static . So i started checking out what all affects the fuse, then i started with the easiest thing to access which was the brake light switch.as i was wiggling the plug adapter and switch the radio display brighten up and started playing good no static. so i replaced with new brake switch, same thing again .so i took out the aftermarket radio completely. and still blows fuse #1. as doing some searching i understand the fuse runs according to manual , multi- function switch bpp (brake pressure position switch) and speed control and as knowing these things i know the wiring also goes through the lighting module . and others also i have disconnected the cig. lighter and i was having this problem before i disconnected the cig lighter. so i was wondering if someone had this problem or know what cause of it is .. hate to spend money on parts not needed. thanks