If you follow Jorrell's advice and you find that it is not charging, the next step is to inspect the wires and ground to the alternator.

If the wiring looks sound, pull the voltage regulator out of the back of the alternator (two screws). Are the brushes (carbon bars) worn down to nubs? If so, you can pick up brushes for $3 and solder them in, or you can spend $30 for a new voltage regulator. Brushes are not sold by part number for these alternators, I took my voltage regulator to a good parts store and a friendly parts man looked through his brush inventory and found a pair that fit.

Also, on an '89, be sure that the contacts on the large spade fuse that is attached to the driver side shock tower are clean. That fuse is notorious for corroding and causing loss of the ignition system. Many folks replace that fuse holder with a marine style fuse holder.

For brick parts, I suggest Autohaus or FCP Groton. Both have great service, quality parts, and low cost. I go to the dealer only in emergencies.