1966 Mustang - Engine Won't Start

Okay, here's my 2 cts. First off, once you release the ignition key from the START position, the power to the S terminal on the solonoid should be gone, which in turn releases the solonoid, so I would try to start the car with it in park, hood open, and if it stays cranking, then pull the wire off the S terminal on the solonoid, and it should stop cranking (if it does, then you either have the wires switched, or have something providing power to that wire during the run position, so I would double check your wires on the ignition switch to make sure you do not have one on the RUN terminal that should be on the START terminal), if it still continues to crank, then take something plastic like the handle on a screwdriver and tap the solonoid and see if it releases, if it releases, then it is the solonoid sticking, buy a better quality one. In addition, the I terminal on the solonoid is a direct connection to the ignition coil + terminal, this is to supply battery voltage to the coil during cranking (START position on the ignition switch), when the ignition switch is in the RUN position, then the coil gets power through a pink resistor wire which drops the voltage to around 6 volts to the coil with the points closed, this prolongs the life of the points and keeps from overheating the coil. A good practice, when replacing electrical parts, is to make sure it is working correctly, before you replace the next one, because if you make a mistake, it will be harder to find, if you replaced several things at a time. Post your results. Good Luck.