First determine whether you have a release relay circuit or just a switch wired directly to the release solenoid. The image showing the release relay location will help. Also listen very carefully to the front of the vehicle when you press the hatch release button. If you hear a click and the hatch solenoid popping then you have a relay if no click is heard but you still hear the solenoid popping then you probably do not.
The release relay is grounded through several switches as you can see by the diagram. The yellow leg coming from the relay coil is the ground but only when the shift selector switch is in the park or neutral position. If any of these several contacts are corroded it will stop the relay from operating. I've also seen some relays with a diode on the ground leg. (A diode is a component which only allows power to flow in one direction.) This diagram does not show a diode because of the way it is designed. This diagram shows the way the engineers designed this circuit to prevent the hatch mechanism from being actuated while the car is being driven or moving down the road. A safety feature I'm sure. If you want to temporarily bypass this design just cut the yellow wire from the relay and ground the relay side of the wire. Be sure and tape off the other side of the yellow wire so it will not ground out.
Also it is possible you have a weak release solenoid or simply dirty connections. If you do not have the release relay design then your switch connections might be corroded. Try running a hot wire directly from the the battery to the power connection on the solenoid. If it pops quickly then you have a ground or power supply connection problem.
As you can tell, diagnosing any wiring problem can be complex, especially when multiple connections are present. I hope the diagrams help you to locate the fault.
MM
