To find it, you'll likely need to:
1. Consult your owner's manual: This is the best place to start. The manual should have a diagram showing the fuse box and relay locations.
2. Look for a fuse box or relay center under the dash: These are usually black plastic boxes with numerous fuses and/or relays. The flasher relay is usually a small, square or rectangular unit.
3. Check online forums and resources: Searching for "1993 Ford Mustang turn signal flasher location" on forums dedicated to Mustangs can yield helpful information and potentially even pictures from other owners.
If you can't locate it easily, a mechanic or auto parts store employee should be able to help you find it. Remember to disconnect your battery's negative terminal before working with electrical components.