VZ commodore: tail lights/electrical question.?

Got a VZ commodore, but the other day the rear tail lights stopped working. When i press the break pedal, the high-intensity break lights come on, but once released, all the lights go out (yes the light switch is turned on as the front lights work fine).

ive checked the fuses, and found 1 fuse which blows up everytime i replace it (according to the diagram, its a 7.5amp fuse which is what i replace it with)...this would be the problem right?

but how do i trace it back to fix the short circuit??? (if thats what it is)