Pre-Face
The Trex 500 is known to produce static with the belt driven tail. This interferes with 2.4GHz radio systems.

Installing a wire to the motor mount screw
A small solid wire should be used along with a thin washer on the frame side to protect the frame. I installed the wire on the inside of the frame with the washer. Face it angled around the motor compartment then run it down.

Measuring

Test for continuity
Use a multi-meter to check for continuity by wrapping the end around one lead and holding the second lead to the inside of the motor mount.

Grounding to the Boom
Run the wire down the bottom of the bottom plate. Then run it back up through the receiver tray right out the back.

First setup your tail and mark where you need to sand so that you can sand the boom. I actually should have been more careful. With no screw inserted you can spread the servo mount with your finger then slip the wire under. Then set your tail up again with the wire under. Add CA one screw at a time to the mount making sure to check it when done.