Not knowing what wiring you crossed, or whether the brake controller you used is even proper for a LR Disco2, I can only point you in some "shot-gunning" directions:
In the passenger compartment fuse box check fuse 25 (15 Amp), fuse 11 (10 Amp) and fuse 33 (10 Amp).
In the engine compartment fuse box check fuse 13 (10 Amp).
You may also have blown out the Park Brake Switch (S215) located on the brake pedal assembly.....
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You may even want to temporarily disconnect the brake controller that you added until you get the original wiring on the truck sorted.
'04 Land Rover Discovery S
Way over 100 Off-Road Treks