Reply to "Help? intermittant won't crank over?"

The P car uses the Mustang/Ford starter relay.

Go right to the relay and jump the big two terminals with the handles of pliers. It will spark like heck but the starter should work right from that point.

If it works there, then get a remote starter switch and connect one end to the big wire coming from the battery, the other to the small terminal that say S. Push the button, does the starter work?

If no, the starter solinoid is done. Replace it.

If yes, then it is one of two things,there is a broken wire in line from the ignition switch to the starter terminal OR (as Marlin says) the ignition switch is burned out.

If the car lays for long periods of time without any use or attention, it may be just the contacts in either are corroded. Both are common.

The ignition switches in these cars were designed to have large voltages run through the ignition switch. That is a bad thing and after 40 years will kill the switch for sure.

Consider installing the Pantera Electronics ignition switch controller. It reduces the loads through the switch. Not convinced. Look at what a new switch is going to cost you and consider you will have to do it again if you don't reduce the loads through it?