I am with rapid on this one. If you've pulled the wire off the brake light switch that feeds the brakes power, then somewhere in the wiring, another circuit that's hot all the time (assuming brake lights are on without the key in the "on" position), then some other circuit is giving it power.... an "always hot" circuit. That narrows it down some.

Step #2, pull "always hot" fuses like Rapid suggests which narrows it down more.

Step #3 maybe take a look at the big (6-prong?) plug, behind the driver's kick panel, that leads back to the tail lights. If you unplug it & the brake lights go out, then it has to be one of those circuits crossed. While unplugged, check to see which one(s) is hot and you're narrowed it down even further......one of those hot wires must be crossed with the brake light somewhere.