I repaired a Squire recently with a bad Hum:-

The volume control had worked lose on the plastic - someone had tightened the volume pot locking nut and in doing so the rest of the pot underneath the scratchboard had turned jamming up against wooden rebate shorting the terminals - by the time I got to it they had been at it with a soldering iron and they had wired the terminals of the output socket the wrong way round { Reversed polarity}
I touched a piece of wire with the guitar plugged in from a Pot body to the Jack plug body where it enters the guitar and the hum disappeared - I then checked the polarity.
Let me know.........