Dead short in Rear Light/Instrument light

Yesterday my recently installed alarm system went dead, along with my rear lights ('tho not the brake or turn signals) and instrument lights. The fuse was blown, and when I installed another (with the lights/power off) it blew again immediately (even with a 20A fuse.) The alarm is on a different fuse which blew when the parking lights blew, since it's wired to flash the lights when it arms. I took it back to the alarm dealer and they spent almost 2 hrs cleaning up the wiring and searching for the short, but found nothing.

Any ideas/suggestions?

I just recently had an issue with that same set of lights - though i traced my problem to a broken ground wire (earth) that goes from the parking/headlight switch to the first(white) block connector behind & above the steering column. I didnt blow any fuses - had no ground between the switch and the tail-light relay.

Years ago I blew a fuse in my VX which took out the tail lights and console lights. I replaced the fuse only for it to blow as well. After taking half the car apart my mechanic found the culprit. It is worth mentioning since more than a few of us have had the same problem.
We found that the wiring harness behind the left headlight had slowly been rubbing against a bracket and finally caused one wire to ground out. Not an easy fix due to where the harness is located. The wire was located, fixed and never had the problem again.