Need location of the fuse for the tag lights on a 1991 mazda 626 dx

The fuse that protects the tag lamp is the same fuse that protects the tail lamps. It is in the under-dash fuse block: marked TAIL 15amp
If the tail lamps are operating, you probably need a bulb. If the bulb doesn't fix it, inspect the tag lamp harness for damage or the lamp socket for corrosion.