According to the 1990 wiring diagram -- and I doubt the '89 is appreciably different -- F9 is switched via four relays, and powers the horns, auxiliary water pump, the phone alert (which just fires the right horn), and the A/C compressor clutch. I'd be inclined to suspect the A/C compressor clutch and related wiring first. Try unplugging it at the compressor. If that doesn't change the problem, then unplug the aux water pump under the heater valves on the left-hand side of the firewall. If that still doesn't do it, you've probably got a cut in the wiring harness somewhere. Then you'll either need to start tracing the wiring from F9 out or from the A/C compressor, horns, and aux pump back to F9.