I agree, FIRST check all connections and make sure they are clean. While you are have the problem, if you are familiar with a Digital Multi Meter, meter the starter wire in the ignition harness withe the key in the start position to make sure its getting twelve volts. Next would be to find the starter relay and see if its getting its 12 volts, or if its even clicking for that matter. If its getting the signal and not clicking, replace the relay. They are usually your typical bosch relay.

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1989 Ford Ranger XLT: Extended Cab, 2.9 V6, 5-Speed
MECP Advanced Certified Mobile Electronics Installer