WARNING: This page is about a different car, the 2004 Buick Regal and 2004 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Rear Compartment Lid Switch & Electrical Connector
Courtesy of GENERAL MOTORS CORP.
Connect the electrical connector to the lid release switch.
Press the lid release switch into the I/P opening.