Starter silenoid

Could be the starter, starter relay, transmission position switch and ignition switch assuming the battery condition and connections are good.

Some of these had 2 solenoids.1 on fender under hood and another on starter itself with the fixed magnet mini starter. Only ford? Better idea? Try tapping on starter with hammer/big wrench to see if it catches. This would mean your starter brushes are worn out. You can buy the brushes but they may not be easy to find.I got some on ebay. $12 at the time. Or replace starter itself.

Also make sure battery has good/full charge.