Sounds to me like the alternater is wired in after the ignition switch. That will keep it from shutting off and will also supply hot power back thru the alternater to the coil. And yes they will explode if the power is on and they are not being ran. I had this happen in a dirt car I got out and bumped the switch to on without the engine running. About 30 minutes later or so and boom. What a frikken mess!