[ss#4]

First thing is this a manual? if so it is probably the backup switch that is thread into the transaxle and activates the lights when the shifter is put into reverse when the key is on. Easy to find and easy fix, just need a 22mm wrench or socket depending on the exact location and clearance. my bet is for the socket with a long extension. The switch is cheap $11 and about 5 minutes, which includes pulling into garage and popping hood.

If it is not a manual then start tracing the harness for a broken wire. Also check the connector at the bulbs, the terminals maybe open too far and not making connection.

IF you can't get this fixed before your trip, don't loose any sleep over them they are a convience item not a safety item.