Shielding A The Telecaster In Foil
Step 1) Take off the pick guard, control plate, output jack and bridge plate. Then, unscrew the pick-ups from the body. At this point, in order to remove the electronics and the pick-ups, you have two choices... either... de-solder each pick ups' wires from the switch and pot to which they are connected (later, re-soldering the wires to their original places)... or... you can do what I did and just cut the pickups' wires about 2 inches from where they connect to the switch and pot (later, reconnecting the wires with a "pin and socket" connector). The benefit of using "pin and socket" connectors is that you will not have to de-solder those wires next time you want to remove the pick-ups or electronics.
Step 2) Using Q-tips dipped in water, clean the exposed cavities. This ensures that the glue will hold the foil on.
Step 3) Choose the cavity which you want to shield first and then cut a piece of foil big enough to cover the entire cavity. Apply the stick of glue to either the cavity or the foil itself in preparation of the application. I find that it is easier to apply glue to the foil than the cavity in cases like narrow wiring cavities.
Step 4) Apply the foil (glue side down) to the cavity. Start by centering the foil over the cavity and then pressing the foil against the bottom-center of the cavity. From the bottom-center of the cavity, carefully press the foil down in all directions, towards the bottom-sides. At this point it may be helpful to use Q-tips to work the foil into the corners of the cavity. Once the entire bottom of the cavity has been covered, press the foil against the cavity walls and then over the edge, onto the front of the body, leaving about an eighth of an inch of foil going around the outside of the cavity. After you have finished the first cavity, continue shielding the others using the same process. In the first picture below I have just finished the neck cavity and I am using the same piece of foil to shield the wiring cavity. I do this because it means one less piece of foil to make sure contacts the rest of the foil. In the second picture you'll notice that I didn't make an eighth inch foil lip around the control and bridge cavity simply because the foil would stick out from under the control plate, when complete.
Step 5) Poke a hole in the foil to expose the wiring holes which have been covered. Then, use the same technique for applying foil as mentioned above, and cover the underside of the pick guard with foil. The foil only needs to cover the places that are directly above the cavities but it does not hurt to do the whole thing.
Step 6) If you decided in step 1 to de-solder the pick-up wires rather than cut them, then skip this step and re-solder the wires to their original places but after step 6 (it should look like the first picture in step 8 but without the connectors). If, in step 1, you decided to cut the pick-up wires, then this is the step in which you solder the pin and socket connectors to your wires. As you can see, I slide a bit of heat shrink tubing on to the wire of the pick up and then crimp on, and solder the male connector. I make sure to use the male connectors on the pickup wires because they are smaller than the female connectors and will fit through the narrow wiring holes in the guitar. I then heat shrink the tube over the soldered part of the connector so that when the female and male connectors are together, there is no exposed metal. Now you can feed the finished pick up wires back through the guitars wiring holes.
Step 7) Before re-mounting the pickups, run a wire from each pick-up cavity (green wire in picture 1 and 2) to the control cavity (picture 3). This wire (the green wires in picture 1,2 and 3) will be the ground connection between the different cavities and will ensure that all of the foil is connected via a conductive material. To get around the un-solderable qualities of aluminium, I have come up with two solutions... an O-ring on the end of the ground wire (picture 1) which is held tight against the foil when the neck pick up is re-mounted... and... an exposed ground wire (picture 2) which is held against the foil when the bridge is re-mounted. Lastly, connect the two pick up cavities ground wires via o-ring (picture 3). The o-ring needs to fit around the shaft of the volume pot in order to press against the control plate, completing the connection between all of the foil.
Step 8) The last step is the re-assembly. Unscrew the volume pot then slide the o-ring (picture 3 of step 7) onto the shaft and re-mount the volume pot. plug in all of the connections as they where before the mod or... if you decided in step 1 to de-solder the pick up wires rather than cut them, now is the time to re-solder them as they where before the mod. Lastly, re-mount the pick guard, control plate, output jack and bridge plate, checking to make sure that no foil sticks out.
Check if the problem is described here, Troubleshooting Guitar Wiring.
If you still have not found the problem, I suggest you join this forum, The DIY Stomp Boxes Forum. It is an incredibly helpful resource that I have recently started to use when I need help troubleshooting. As long as you are polite and give a detailed description of the problem you are sure to get some valueable help within a matter of minutes. Most people on this forum are far more knowledgable about active electronics than I am and will be able to help you better and faster than I could.