I used to use a tester from Snap-On that is a circuit breaker with an amp/inductive gage. When you hold it over the wire it tells you which direction to go in to trace a short to ground condition.
Since, I have stopped working at dealers, I have rarely run into a short to ground condition. It is kind of a guessing game. You can disconnect the harness from all the park lights all at one time. That would seem the easiest first step. If you fuse does not blow, then plug them in one at a time. Otherwise, keep looking at the other areas including the light for the cigar lighter.