1997 Ford Taurus car wont start

When you say it has trouble what kind? Clicking? Or nothing at all? If you hear a click, then either the battery is weak, or the starter, possibly bad battery cable connections, check and clean both ends of BOTH cables! Dissconnect negative(-) first, and put it on last! If no click the starter relay is no good! Does it turn over(crank)?

Follow your Positive battery cable, it takes you to the strter solinoid, try crossing the small red/green wire terminal marked "S" to the post with the batt cable attached to it, do it with a pair of needle nose pliers or a large diameter wire, dont dissconnect any wires from the solinoid, have the key in the on position, if car starts replace the solinoid.