I recently put a set of Texas specials in my gigging squire. At the same time I put an on/off toggle switch in so i can combine bridge & neck pups (tele factor). I ran wires from the 5 way switch neck & Bridge pos to the toggle switch. I earthed it by soldering a wire from the casing of the toggle to the top of the tone control. Now I have a buzz. If I touch the toggle, the jack plate or the 5 way switch screws it stops. I also insulated the control cavity with foil. I have done all of this before on other guitars and have never had this issue. The only other mod that I did was reverse the angle of the bridge pup (Hendrix factor)
Please help? I gig every weekend, and the last thing I need in the pub scene is another distraction.
Sounds to me like you've got a bad connection between the upper and lower portions of the shield. When you re-assembled the guitar, you may have knocked something askew. Also, you didn't mention that touching the strings causes the buzz to disappear. If that's not happening, then the ground wire out to the bridge/trem claw is not properly connected. That also could have been sundered when putting thing back together, but it's not near as likely. Double check the quality of the solder joints.
After you've inspected for, and made any corrections to, any possible bogus conditions, don't reassemble the guitar just yet. First, plug the guitar into an amp, and turn it on. Got hum? Good. (Make sure the guitar volume is not all the way down.) Now carefully position the scratchplate onto the guitar. The moment the 'plate shielding touches the cavity shielding, it should get real quiet. If that doesn't happen, then your friend Mr. Murphy is still inhabiting the guitar's innards.
Stand back and take a deep breath. Then call a friend over to have him/her look at it. A fresh perspective might see something you've missed.
Oh, and by the way, to the forums!
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You are a legend mate! I checked the ground wire out to the bridge/trem claw and guess what - it had been disconected. I grabbed the trusty iron and put it back on. I only have the slightest hum now when I flick the toggle switch on. If I put my hands on the strings it goes. Man I can live with that!