You say the fuse now blows almost immediately, right ?
I would first remove the brake relay and drive around a parking lot or something ( NOT public streets/roads ) to see if the fuse still blows immediately.
If it does not, then I would then try replacing the relay to see if this resolves.
If that doesn't do it, then it has to be a wire going to the left/right/top stoplight from the ICM ( light switch ) being shorted out.

This is where it gets interesting.
The schematic shows that pins 5,6 and 7 of the light switch ( illumination control module ) supply voltage to the left, right and center brake lights.
You have to disconnect the plug from the module and use a meter to measure resistance to ground from these pins.
First, remove the bulbs and disconnect the high mounted lamp.
Using the multimeter's beep function, connect one lead to pin 5 and the other to a good ground. ( follow by also testing pin 6 & 7 )
open/close doors, trunk lids etc and wiggle whatever wires you can get your hands on.
If you hear a beep, that indicates a short to ground in that circuit.
You're kinda on you own from that point in locating the short, sorry.

BTW, you can download the entire service manual from the below link(s) in my signature.