First of all Welcome to the Bronco Zone!
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I would guess the bulbs would be either 1156 or 911.
If you don't know the difference, the 1156 is a taillight bulb with 1 filament and the 911 is a marker & dashlight. The 911 also is small in size with a flat mounting surface. The 1156 mounts into a socket about the diameter of a dime.
The bulbs may be out of the lights because of an electrical problem so be careful when you install the new ones and expect them to blow out.