Your son should be able to disconnect the harness connectors himself. There is one under each hinge, accessible when the headliner is pulled down to reveal them. Here is a picture showing the headliner pulled down under the left hinge:



You'll see the headliner has a black plastic retainer sewed to the edge of the headliner. This fits over a metal track and keeps the headliner attached to the top of the car. To remove it, grab the headliner in the corner where it disappear into the the roof, and gently pull out and down. You'll feel it start to move, and then gently work your way outward on both sides of the corner to remove the headliner. Do this on each side.

Once it's removed, you'll see the connectors for the tailgate wiring. Here's a picture of the connectors on the driver's side:



The passenger side also has connectors that should be disconnected as well.

You can either disconnect all the connections and test, or try one by one to see which (if any) cause the fuse to blow.

If, after disconnecting all the connections, the fuse still blows, there is a short someplace else.

Let us know what happens.

Thanks.