Phil,
Well you've sort of done some troubleshooting already: the fuse blows when you turn on the parking lamps. This will turn on all your dash lights and all your (duh) parking and marker lamps. First thing I wold do is check every lamp on the outside of the vehicle that is supposed to come on in the parking lights position. Remove the lens covers and check for water/moisture contamination and corrosion....clean any socket that looks crudy and give em all a shot of WD40. Check the condition of the sockets and replace all the bulbs as you go through the check. Try to look underneath the vehicle and see if there is any cut insulation on the wiring immediately leading to the bulb socket.
I doubt it would be anything in the dash since you indicated you'd not done anything (aftermarket stereo, etc).
Does your Jeep have trailer hitch wiring? If there is a harness make sure those wires are not shorting out or the plug end is not grounding to the chassis. Even if your Jeep doesn't have a hitch, the previous owner may have had one on there and removed it (or the dealer removed it) but left the wiring stuffed up under the bumper. If you find a harness w/o a hitch and you don't plan on towing I would remove the hitch wiring.
Hopefully you'll find it's something simple like a bum bulb or socket or moisture.
Good luck....
Mike
00XJ