WARNING: This page is about a different car, the 2008 Buick LaCrosse and 2008 Buick Allure. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Rear Door Rubber Conduit
Courtesy of GENERAL MOTORS CORP.
Install the rubber conduit (1) to the door.
Connect the electrical connector.
Install the rubber conduit (1) to the center pillar.