1) You are making assumptions that are wasting your time. The "liftgate" sense is pin 13 of connector C1 on the CLP/SSM. This tells the security system that the liftgate (trunk) lid is open or closed. This pin does NOT control the trunk light.

2) What year is the car?
2005-2006: Trunk light is wired to the interior light circuit (dome light), not connected in such a way that the ECU knows that the trunk is open. There is a separate switch that drives the "trunk open" indication.
2007-2008: This one is unknown, I know the trunk light does not drive the dome light at all but I can't say exactly how it is wired. But it would in contrary to their designs for the trunk light switch to drive the CLP/SSM "trunk status" indication; not saying it is impossible they did that, just unlikely.

3) If you want to get into this, I encourage you. But you MUST get the service manual out and start going thru the diagrams so that you understand how the systems work. EXAMLPE: Being distracted by the trunk light being on is a rookie mistake that will waste DAYS of your time. I urge you to sit with the wiring diagrams and read - this will raise questions in your mind that you must clarify before proceeding. I've been here 15 years and I an still uncovering oddities - like I had no idea the trunk light wiring varied until I bought my 2007 Roadster and observed some differences that everyone said did not exist; all Crossfires are not wired the same, changes were made in 2007.