Yeah, on at least the mk1s, mk2s and mk3s the ignition switches are really fragile and what seems to go out a lot is the 'hot in both start and run' circuit. There are several terminals on the switch, the battery input and 'hot in run,' 'hot on start' and 'hot on both start and run.' This leads to a situation where the starter works normally, all the accessories and systems work normally in the 'run' position but power is cut to those which need power in both 'start' and 'run,' except the starter, which gets power only for 'start,' so the engine cranks and things test out fine but it won't fire, this affects both gas and diesel models. I've also seen the 'start' circuit not disengage and the starter keeps going. I don't know about the mk4s though.