I'd say wiring harness too. Mine had the same problem. It didn't start once or twice then started fine a few minutes later until one day it wouldn't start at all. It's a known problem because the mechanic at the dealership walked out to mine, popped the hood, reached in and jiggled the wire, hopped back in and started it to drive it into the shop. He parked it right next to another XK that was there for the same thing.