I drove an old Furd F350 tow truck in college. The ignition switch was so worn, the key would fall out while you were rolling, and once when I hit a bump, the thing turned itself off. I just turned it back to the 'on' position. Big mistake. All the unburnt fuel collected in the mufflers and one spark lit the whole column of mix and I blew out both mufflers while a customer's car was on the hook, loud as hall all the way back to the shop. I was pissed when the boss made me replace them. Oh well, it was on his dime, and I got to use the lift.