Isuzu Trooper High Beam Malfunction

I have a 91 Trooper that has a short somewhere in the lighting system. The taillights/dash lights are on the same fuse and when I turn on the headlights, the fuse burns out. Additionally, my highbeams don't work. When I push the switch for the highbeams, the lights go out completely...when I pull it back they come back on. I thought it was a faulty highbeam relay and switched it with another... the problem is the same. Could it be the headlight switch itself, or is there another realy under the hood? All other lights work fine so it seems to me that the problem is centered around the highbeams and running lights. Any info would be great! Thanks, Joe