I have a 1964.5 289 convertible mustang starting problem. When you turn the key to the start position the car starts but won't stay running when you let the key go. I installed a new ignition switch & solenoid but still the same. A wire in the dash gets hot if I try to hold the key in the start position.
There are actually two circuits going to the coil. And you have only one working.
When the car is trying to start, the second small terminal on the starter solenoid is feeding 12V to the Batt side of the coil. This gives you a hot spark that is hard on the coil and the points. When you release the key, then the nichrome resistance wire coming from the "on" portion of the ignition switch takes over and supplies lower resistance to the coil. You may have a bad ignition switch or the resistance wire has parted somewhere inside the dash. Disconnect the second terminal of the starter solenoid, the small one closest to the hood hinge, turn the key on,and start tracing wires looking for power at the switch and then through the harness.
Bad wire between switch and ignition coil.
Bad wire between switch and ignition coil.
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