In electronic terms most shielding is always connected to the zero volt line, If memory serves me correctly, split supplies such as +5 and -5 volt systems, +12 and -12 systems will have a 'ground' at 0 volts.
Single supplies in normally every case (and this should include the QL) that have a 3 pin voltage regulator, such as the 7805 (just in front of the microdrives on a heat sink), would be connected as follows:
Pin In – raw input voltage
Pin Out – regulated output voltage
Pin GND – connects to ‘0’ volts hence Ground and also shield
Diagram here
http://www.national.com/images/pf/LM78M05/01048409.pdf
On most circuit diagrams general practice would be to have the ground connection as the most expanse of copper that you see, however it is not always the case.
If you trace the GND pin on the regulator to some point where you can attach a cable, or alternatively the black cable indicated here on the underside of the keyboard
https://picasaweb.google.com/1087615291 ... 6513300162 this can be your connection to the shield that you put within the QL case, however it must not touch any other electrical connection, as this will short out and cause damage to your QL.
Alternatively you could run a cable from your shield connection to the big shiny metal
case of the RF modulator. I will try and post an image later.
I am doing this from work without actually checking, so please if your not sure, refrain until confirmed by other people.