It's a wagon but I catch your drift about the rear lock. As a matter of fact.....

I have a case of the perpetual "tailgate open" annunciation at the DIM which I was investigating last weekend. I got into the tailgate latch assembly expecting to find a bad micro switch or loose wire or ? But the switch checked out OK and the lock solenoid functioned properly, etc. Nothing appeared awry in that area. I also opened up the plastic boot that protects the wires past the tailgate hinge. Everything looked good there also. Hmmm, I wonder if I might have pinched a wire in the process - was pretty darn careful not to. It was intersting to see the latch open/close micro switch is wired in series with the tailgate glass breakage sensor. Normally, the circuit is closed, running to ground after the glass sensor. If either the latch sensor micro switch opens OR the continuity to ground through the glass sensor is interupted, presumably it's displayed on the DIM and triggers the alarm.

Anyway, you just gave me a third place to investigate for a ground. And as much as I hate to admit it, anywhere that I've recently been probing and prodding becomes the most suspect.