If you still have bulbs in any of the running lights and/or tail lights the ohm meter will give you the impression there is a short. When the filament in the bulbs is cold there is very little resistance.
Before you tear the skin off of the inside make sure you don't have any problems with fixtures, tail and clearance lights. Even with the bulbs out you may have a shorted socket.
Knowledge: "A gift to be shared. A treasure to receive."