Fuses are for backup lights.
You have a short in the wires going to the bulbs.
15 years old... do you off road it? Check the bulb sockets from contact to ground. They may be corroded to the point of shorting out. Look at the fuse diagram and see what else is protected by that fuse. You will need to check each item on the circuit for a short.
Looking for a Used Ranger in your area?
CarGurus has 5,805 nationwide Ranger listings starting at $1,650.
Search Ford Ranger Questions
Ford Ranger Experts