I suspect the liftgate ajar switch (rear hatch open switch) might be faulty since I have two problems that might be related:

1. The interior lights stay on even when the doors are closed (so I leave the dome light switch off),
2. The rear spoiler doesn't deploy.

This has been the case for a couple of years. I'm not sure that these two things happened simultaneously but I think they might have.

I'm trying to find a test point in a harness where I can open and close the liftgate and test for continuity (or voltage) but haven't found that signal in the shop manual wiring diagrams.

Has anyone been through this? Any techs out there with knowledge?

Yep, I bought my Crossfire new nearly 14 years ago.