Triumph Repair: Super Coil, ballast resistor, triumph spitfire

Question
I have a 1970 Triumph Spitfire.  I am in the midst of putting in a new wiring harness on all systems so that everything is new.  I thought all was going well until  I took a break and came out to see that the super coil was steaming and a crack occured allowing hot oil to spray.  Why, with the car all the way off except for the accesories being left on at the ingnition switch, did the super coil explode basically?

Answer
Hi Kevin,
Something is wired wrong as I never seen a British car have the ignition on in the ACC position. So first thing to do is test the white wires on the coil to see if they are hot (disconnected from the coil) with the key in the ACC position. If so you need to get out your wiring diagram and start tracing from the coil back to the ignition switch to see what is wrong.

Unless you made a mistake and had the ignition switch on Ign. A 70 Spitfire had points in the distributor and the ignition can be left on IF the points are open but if they happen to be closed and left on it will over heat a coil even if the correct coil is used. (12v coil is used with no ballast resistor and a 6v coil is used with a resistor) (some coils don't say if it is used either a resistor or not so you should use an ohm meter to check across the two small posts. If it is about 1.5 ohm then it is a 6v coil. If it is up around 3.5 ohm then it is probably a 12v coil to be used on an application that does not use a resistor.
Howard