If the switch you are useing is a standard Fender switch
http://www.fender.com/support/diagrams/pdf...0134600DPg2.pdf
If you are useing a Stewart-Macdonald switch
http://www.stewmac.com/shop/Electronics,_p...91.html#details
If it's not a switch problem, check all your solder joints and make sure wires aren't coming in contact with each other causeing it to ground or short.
If it looks sloppy, clean it up and you'll probably find the problem.