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Igniton switch cuts out

When I go to start my 1988 truck the only way to keep it running is to barely turn the switch back from engaging the starter. If I hold it in this position it will run. If I let it go to the normal run position it immediatly shuts off the engine. I tried replacing the ignition switch, but same thing happens with a new stitch.

The problem is with the ignition module. Ford’s of this vintage were infomous for this.

Ignition modules operate in two modes. These are the start and run modes. When the ignition switch is turned to the start position, the ignition module allows full battery voltage to the coil. This ensures that a cold/rich engine starts. Once the ignition switch moves to the run position, the ignition module switches to the run mode. The ignition module then drops the voltage to the coil because once the engine starts, it takes less voltage to keep the engine running. And it also saves on the wear and tear on the secondary ignition components. (coil, cap, rotor, plug wires. and sparkplugs)

If you can keep the engine running by manipulating the ignition switch, I’d say the start mode of the ignition module is functioning properly. But the run mode has failed.