Rap on the starter with a hammer or pipe. Don't get carried away.
If that works, your starter's shot.
If that doesn't work, it could either be a bad starter or a bad cable TO the starter. Disconnect the battery first if you are going to replace that cable or the starter.
Most AP stores can test your starter for nothing.
It could also be a bad battery cable, + or -, they like to rot under the insulation. You didn't mention what year, so I don't know if you have a fender mounted solenoid relay or not. They go bad too.
2000 2.5 MO5D 4.10 one-wheel drive DD - gave to my older son
1990 STX 87 2.9 going in.....Junked it
2000 3.0 4WD M05D 4.10 S-cab Off-Road package with 235-75-15" tires, hotrod DD, lol