No, you don't need to use a gauge to install spark plugs in a 1996 Ford Windstar. There's no adjustment required beyond tightening them to the proper torque specification. Using a torque wrench is crucial to avoid over-tightening and damaging the threads in the cylinder head. Over-tightening is much more damaging than under-tightening (though under-tightening can lead to misfires).
Consult your owner's manual or a reliable repair manual for the correct torque specification for your Windstar's spark plugs. This specification will be in pound-feet (lb-ft).
