Using the guidance offered, for which thanks, I’ve come to the conclusion that I don’t have a ballast resistor. Wires from the coil connect to the distributor or straight into the wiring loom which disappears (or appears, depending on which way you are tracing it) into the bulkhead by the fuse box.
Not sure what this means for the spec for the coil, if I’m to replace that, but if I can get it off I might be able to find some identifying codes on it.
Mark
I wonder if you've got a 9 volt coil and, as Arwyn suggests above, someone's removed the ballast resistor in the past leading to 12 volts going permanently through a 9 volt coil and the coil overheating. This could explain why the car fires when it cools down.
If it's a Lucas coil it should have something stamped on the bottom.
