MG Car Repair: MG wiring mystery solved!, ballast resistor, jumper wire

Question
hey Barrie you're right on- I tested and found 13V engine running and then realized that indeed a short jumper wire was run direct from #3 fuse to the + side of coil. ( probably my mechanic who was tinkering with it few weeks back ) The other + terminal is connected to 2 White \ Lt green wires - one goes to fuel pump - other disappears into harness and connects to red resitive wire and then red wire looped back to fuse area and was just hanging there. so - I disconnected the short jumper wire and tossed. I connected red wire directly to #3 spade connector. Car runs beautifully! 9V output now and no bogging, backfiring. I would like to send you box cigars - alas rules do not allow.  THX,  ps the coil is old and label worn off but the casing is stamped 12V and cab see worn instruction to 'use with ??.res.??..' can't make out after that. Could I have damaged it? It burned pretty hot.
Paul

Answer
That's great, Paul.  

My guess is that the label says "Use with a ballast resistor".  The only way to confirm this is with an accurate digital ohm meter.  You need to disconnect the wires before you start.  If the resistance between the two small terminals is around 3 ohms then you have an ordinary 12 volt coil.  If it is around 2 ohms then it is the correct ballasted 12 volt coil for your car.  If it is around 1 ohm then the coil is designed for use with electronic ignition only.

Coils do get hot, and running it at 13 volts will have overheated it, but it still works so I reckon you have gotten away with it.