Make sure your starter solenoid is a real live FORD made part. Crap from Autozone etc. tend to weld their contacts together of a regular basis. True story.

On the flip side, the real live FORD made ignition switch on the column, not the one you stick your key into, is a total POS in it's original form. If it has never been replaced...even with an Autozone one, now is a good time to do it. They are cheap. The original ones are dangerous. More than a few 80's and 90's Fords have burned up just sitting in the driveway.