if the garage is saying they were ignorant to this fact that is a bit worrying, make sure they check all the parts related to the washers as surely this means everytime your lights were on and you sprayed your jets, your headlight washers were banging into the bumper, this may have caused damage, of course if this wasnt happening because the thing wasnt wired up at all then that proves the garage are twats and knew all about it from the beginning as they knew to disconnect it!