Power Liftgate Rear Control Switch - Quarter Trim Panel
WARNING: This page is about a different car, the 2007 Lincoln MKX and 2007 Ford Edge. However, it is still accessible from the selected car via links, so may be relevant.
Pressing the power liftgate rear control switch (located on the LH quarter trim panel) supplies a momentary ground signal to the LTM which will operate the liftgate depending on the conditions.