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

Since the radio static changed when you wiggled the brake switch plug, I would look hard at that connector and the wires right behind it before buying anything else, because a new switch on a damaged plug or chafed wire will act exactly like the old one.

To find a short that keeps taking out a fuse, pull the fuse and put a test light across the two terminals of its socket. It stands in for the fuse and acts as a load. Turn the key to run: if the bulb lights up bright, something on that circuit is grounded. Then unplug the loads on fuse 1 one at a time (brake switch, multifunction switch, speed control), and when the bulb goes dim or dark, you have found the branch with the short. If it only flares when you move the wiring, wiggle each section of harness while you watch it.

Our 1998 Crown Victoria and Grand Marquis instrument panel fuse chart lists what each fuse feeds, so you can see everything that shares fuse 1:
https://www.supermotors.net/reference/ford/crown-victoria/1998-2011/fuse-relay-charts

Dana