When I shielded my guitar I managed to kill the sound completely.
I had an EMG 85, 1 volume, battery and a stereo output jack all wired up and working correctly, but when I touched the pickup with my finger there would be a buzz so I decided to shield the pickup cavity as well as the control cavity in the back. When I did there was no sound at all, unless I unplugged the cable most of the way, then there would be sound, but the volume control seemed to be bypassed as the volume didn't change no matter where on the dial I turned it to.
When I pulled it apart I tried it again with the volume control hanging out the back, but with everything still wired up exactly the same, and to my surprise it worked again, the only difference being the volume pot was no longer in contact with the shileding paint.
After searching here on pg for similar threads I see that it might be caused by a ground loop or wiring things to the wrong place - and that's what it turned out to be. I am using a flush mount output jack that came with no instructions so I had to guess which lug was which. When I switched two of the wires around it worked in reverse to how it had been before ie, when touching the shielding paint it would now work when the cable was plugged all the way in.
The only thing that still confuses me is the ground wire between the volume pot and the out put jack - it makes no difference if it is even connected or not. I tested the guitar before connecting it (so only two of the three output jack lugs were connected) and it worked perfectly with no buzzing or cutting out. I connected it any way and it still works with no problems.