I have a 08 Navigator with power liftgate. It will open and close with the button on the dash, as well as button on the remote (double press). But it won't open or close with the button in the "trunk" (located about 1' away from the liftgate on the driver side), same with the button on the exterior handle. For the button in "trunk", when I press on it, there is this long beep sound and nothing moves. For the button on the outside handle, I can hear some mechanism and I can open the gate manually and lift it up. but it's supposed to be automatic!.
So, to me it should be some kind of control or electrical issue. But I don't know where to start. Any ideas?

 

Check fuses 14, 17, 27