Hot coil

[waltmgb]

77 MGB w/Pertronix ignition. I know the coil gets quite hot when running. But should it be hot with just the ignition on? Seems it shouldn't be drawing current so shouldn't heat. What am I missing?

[Vic Butler]

How long is the ignition being left on? It's not a good idea to do so as the coil will overheat. If you have to leave the ignition switched on for a long period without the engine running then the feed wire to the positive coil terminal should be disconnected to avoid this happening.

[waltmgb]

Thank you. That's the information I needed.

Walt

[Not_Anumber]

How long are you leaving it on for ? If its boiling hot after 2 or 3 mins then that's wrong but if it was left on for hours then it could be expected

[Vic Butler]

When I was trying to get my Land Rover windscreen washer pump to work I had to leave the ignition on for a short period but I didn't think of checking the coil. This has Pertronix electronic ignition fitted too with a recent NGK coil.
Presumably you have the correct ballast resistor coil with an impedance of around 3 ohms. Easy to check with a multimeter.

[waltmgb]

Thank you all. I do have the correct ballast resistor and the coil gets hot after about 1/2 hour. I'll just disconnect it. That works. And I'll revisit this after fixing other electrical issues. Watch for those threads coming up.

[Vic Butler]

A few minutes is ok but half an hour is far too long for the ignition to be switched on without the coil being disconnected.