W126 alarm - odd behavior

[LandYaghtLover]

Pretty sure I will have to check every little thing, but just running this by you all incase this exact scenario sounds familiar.

Alarm goes off when I start the car. It does not go off when sitting armed.

If I turn the trunk lock to 3 o'clock, I can unlock the driver and open it and press brake pedal. But if I open other doors or trunk it will go off.

If I turn the trunk lock to 9'oclock, I can unlock the driver door and open it. But It seems to go off when I press the brake pedal or start car. However once unlock I can open any other door without it going off.

In any case, closing doors then locking driver door stops alarm.

Main suspect is the trunk lock tumbler since one position is suppose to kill the alarm, correct? I am guessing this exact issue is not common and I will simply have to remove all the door panels and such and check every little inch of the system.

This is a replacement module I am installing, the car has not had an alarm since I bought it. There is an aftermarket radio installed.