Hi Pirate and All!
Thanks RickNelson I forgot to include the type and "how to install" part! I will check with one of our RF/RFI/EMI "experts for the grounding of the gear box you have me curious about this. Typically there are the "most likely" causes of things going "spritual" on you. Probably the most common cause of problems is the 5-6 volts supply for the receiver and servo connection box. This is especially true if you are using a BEC to provide the lower voltage say in a 12 volt setup. BEC's are made to be cheap and often a very necessary 1 uf tantilum capacitor has not been installed. BEC by their nature "oscillate" at frequencies upto 400 Mhz and can have modulation on this oscillation! So you have a transmitter you do not know about!
It would not hurt to add some .1 mfd caps on the servo power leads or you can remove the servo connector and run the wires through a ferrite donut. Mc Master-Carr has copper foil tape with conductive adhesive. http://www.mcmaster.com/#copper-foil-tape/=5ddn98
As for ground wires, the most direct path to the main battery negative terminal is best. What to avoid is creating a "ground loop" by grounding the motor case, mechanically connecting the shaft of the motor to the gear box using only metal couplings and then having a ground wire on the gear box! Then you would have a ground wire that starts from the battery negative, to the motor case, with the motor shaft connected to the gear box and a wire back to the battery negative or one big loop which should be avoided at all cost. For your servo, probably take a make a hole in the copper tape for the servo shaft, wrap the tape vertically around the servo, then wrap another piece of copper tape horizontally. Since the copper tape has conductive adhesive everything will be good. Then yes, solder a ground wire to the copper tape and run it to the battery negative. A note about ground wires. They need to be as heavy a gauge as possible. If you are concerned with a large wire bundle, then consider using teflon coated wire as the wires insulation is thinner. Yes, it is a much more expensive wire to use. Why? Because it's worth it!