318i to 325i engine change query

[fastcarz464]

i took my 318 to a garage and asked how much to stick a 325i engine gearbox and diff and they quoted Ԛ£600, he said its a bitch to do the electrics so i told him how much just to put the engine, box, diff and exhaust etc and not the loom, he said Ԛ£200, so ive agreed, what is involved in changine the engine loom, or does the whole wireing loom for the car has to be changed? how hard is it to do? cheers!