* Ignition System Short: The most likely culprit is a short circuit somewhere in the ignition system. This could be a short to ground in the wiring leading to the coil, a faulty ignition switch sending excessive current to the coil, or even a problem within the coil itself (though less likely to cause immediate overheating just from the "key on" position). The current flows through the coil's primary winding, generating heat due to resistance.
* Faulty Ignition Control Module (ICM) (if equipped): Some 460s in 1983 might have had an ICM. A malfunctioning ICM could send excessive voltage or current to the coil.
* Shorted Ballast Resistor (if equipped): Older ignition systems sometimes used a ballast resistor to reduce current to the coil during cranking. A shorted ballast resistor would allow full voltage to constantly flow to the coil even with the key just on.
* Wiring Issues: Corrosion, damaged insulation, or loose connections in the wiring harness leading to the coil can create a low resistance path, leading to excessive current flow and heat buildup.
* Internal Coil Failure: While less likely to cause immediate overheating upon just turning the key, a shorted internal winding within the coil itself could also be responsible. This is more common to manifest as overheating _during_ operation but isn't impossible in this scenario.
Troubleshooting Steps:
1. Visual Inspection: Carefully inspect all wiring related to the coil, looking for any signs of damage, chafing, corrosion, or loose connections. Pay close attention to the wiring near the coil itself, and the connections at the coil and ignition switch.
2. Check the Ignition Switch: With the key in the "ON" position (but not cranking), measure the voltage going to the coil's positive terminal. It should be battery voltage (around 12V) but only briefly, then reduced by a ballast resistor. High voltage, or consistently high voltage (without a drop), indicates a problem with the ignition switch or ballast resistor. Caution: Be very careful when working with electrical components; disconnect the negative battery terminal before proceeding.
3. Check the Coil Resistance: With the key off and the negative battery terminal disconnected, use a multimeter to check the coil's primary and secondary winding resistances. Compare your readings to the specifications for your particular coil.
4. Check the ICM (if equipped): If your vehicle has an ICM, testing it will require a multimeter and possibly a wiring diagram to verify its correct operation and output.
5. Replace the coil: If the wiring and other components look fine, then replace the coil as a last resort. A new coil is relatively inexpensive.
If you're not comfortable working with automotive electrical systems, it's best to take your E-250 to a qualified mechanic for diagnosis and repair. A hot coil is a serious fire hazard.
