I have a 1973 Datsun 240k that will only run while I’m turning the key and engaging the starter. As soon as I let go of the key the car immediately dies

What would cause this?

1 Answer 1


That is usually a ballast resistor fault.

Some cars had a resistor mounted next to the ccoil which provided about 9v to the coil when running. When starting the coil was supplied with 12v to increase spark voltage.

On some cars the ballast resistor was a length of resistance wire built into the wiring harness.

Try putting a supply from an ignition feed source and testing again, if it runs then you need to replace the ballast resistor. Or you can fit a standard 12v coil instead.

  • 3
    Thanks, in my case there was a length of resistance wire that was causing the issue Jan 4, 2020 at 15:17
  • 3
    Note that if you run a 9V coil on 12V constantly you'll cook the condenser inside the distributor. Jan 5, 2020 at 0:22
  • @BobJarvis-ReinstateMonica you did note that I put that one would need to replace the ballast redistor or fit a 12v coil?
    – Solar Mike
    Jan 5, 2020 at 20:10
  • What? You expected me to read the last sentence?!? :-} Jan 5, 2020 at 21:07

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