any time a fuse blows it means that there is a dead short-to-ground that is allowing too high a current flow for the circuit. the fuse is there to protect the wiring to keep it from burning.
take the taillight bulbs out and then replace the fuse. the fuse should not blow with the bulbs out (turn the headlamps on after you replace the fuse). if the fuse does not blow, turn the lights off and put in one of the bulbs and turn the lights on again. if the fuse is still good, then put the other bulb in and try it. when the fuse blows you will have identified what bulb is shorted. (note, one shorted bulb is what usually causes the condition). note: if you have side running lights then remember to remove the connectors from those bulbs as well because they come on with the taillights)
if the fuse blows with no bulbs in the sockets then the problem is with the sockets or the wiring between the headlamp switch and the sockets or the headlamp switch itself. you'll need to narrow it down.
if the fuse blows with no bulbs in it, check the wiring along the back of the car between the taillights and the point where the harness goes into the car. look for any stripped wires or places where the harness may have become pinched. if its not a shorted bulb, you're looking for a bare wire touching metal.
hope that helps
