I'm helping a friend diagnose and repair a problem with his 1943 8N Ford tractor. I had it running great last season, but unfortunately he used his tractor to attempt a jump start with his SUV. He connected the SUV 12V system to the tractor's 6V system. The tractor was running, but when the SUV started, the tractor died immediately. I have checked the battery, the ignition switch, the starter button, the starter, the resistor and all wiring up to the voltage regulator. All appears to function properly. There is no spark to any of the spark plugs with turning the engine over with the starter. My initial thought was a blown coil or bad voltage regulator, but I prefer to not get into a parts replacement mode of repair. Does anyone have a thought about the likely component that failed. The tractor is in a remote location so I'd prefer to buy the parts necessary and do the repair at one time. Thanks for any help that you can provide.