'cutting the wire; makes it sound aftermarket they would never have found any wires if it had been factory fit.
anyone with a basic knowledge of electrics should get past it, just a question of following wires(depending on how well it was fitted) to find out which curcuits have been spliced into, usually just one on the ignition curcuit , fuel pump relay or similiar , just join them up and job done. Its not that difficult just ask the darling little 'twockers' with one brain cell..they can do it in seconds.
Dont really have to even remove the immobiliser,