[font=trebuchet ms]I don't get much from your 'drawing', but from your description I think you've got it pegged. As the pot is adjusted towards the end that is tied to the wiper, the resistance between pins 1 and 3 will reach the maximum value. As the pot is adjusted the other way, the connection between pins 2 and 3 will progressively short out more and more of the internal resistor, until the wiper reaches the pin 1 end of its travel. At that point the resistance between pin 1 and 3 will measure as zero.

The backshell of a pot is not connected to the internal resistor, but it often is connected to the threaded ferrule that mounts the pot to the guitar. Which means that the circuit 'sees' ground via any shielding applied to the control cavity, as well as through the connections on the backs of the pots. These multiple grounding paths form loops which act as antennas for any stray radio signals in the room, including noise from computers, TV sets, and appliances.[/font]