This is a very normal problem. There is a hole in your vinyl to reach with a screwdrive and pop the hatch manually from inside the car.
It's a ground problem most likely. Those used to get ground from a big pin in the back, which rusts and breaks often. Even when it is there it generally only provides a fraction of the ground necessary for a positive click. It is very important to jump a ground cable from the roof to the hatch, usually right there on the passenger side corner where your defrost wire bridges it if you have one. Before adding the bridge wire, I measured 4 volts across my solenoid. Immediately after the wire was added I measured the full 12 volts. It's a huge difference.
I also find that stubborn hatches, or bad grease, or rubbing all work to keep it from opening reliably. I also hate to walk around the car every time I want to get in the back. I add a simple switch in the glove box using the same wires. I then also add a doorbell right up above the license plate. If the switch in the glove box is off, then there is no power sent to the doorbell and the hatch is essentially locked. Turn the glove box switch on and it sends 12 volts to the doorbell, but it doesn't go to the solenoid until you walk around and push the doorbell. This means you are standing right at the hatch when you want to open it, and you can jiggle as you push it if it is ever stubborn.
On my car I actually added a second 12 volt power wire to a hidden switch accessible from outside the car. If I locked my keys out of the car, I would hit the hidden switch and the doorbell would have power even if the glove box switch was still off. Instant car unlock.
Topic: Rear Hatch Release (Read 6103 times)