Did you determine which door is the culprit? The driver information center in the cluster will tell you if it thinks the door is open with key on. My 2006 JUST did the same thing. Driving along and chimes "right rear door open". The dome lights won't come on if you're going faster than 15MPH. My driver door door did this years ago but requires a little more effort due to the key cylinder and window regulator. Anywhoooo, I am going to replace my right rear door switch and photograph the process if you need them posted for your son. It's a simple job, my Dorman switch was $9 shipped from eBay with a lifetime warranty.
'04 Silver Marauder w/ sunroof - HID lighting, JL Audio / Eclipse DVD/NAV/iPod/camera, 4.10's, 2" drop, Progard Bumper Baffle, Delete tips, Billet Pedals, BC4E dead pedal, Lidio Tune, Mach1 chin spoiler, K&N CAI, TCE lines, Super40's, tinted tails, SS Inserts, Heinous Control Arms, Real oil gauge, lighted door handles. Currently installing Eaton M112.
2004 Mercury Marauder
Born March 2004, adopted October 2005. Sold January 2012, adopted AGAIN January 2016
2,187 of 3,214
997 in Silver Birch
448 with light flint interior
304 with heated seats
336 with sunroof