Proper way to use a shield and ground-wire when rewiring a guitar

Question

In an attempt to resolve some major hum problems with my son's archtop with a floating pickup, I'm about to start my 2nd rewiring attempt. This time I'm going to be using 18 gauge, stranded, shielded wire. I've seen a lot of recommendations of 22 gauge but 18 seems like a better size for the various holes and plugs. The wire has a red and black and then a wrapping foil with a single shield wire that can be used to wire the shield into the circuits.

Questions:

1. Is my choice of wire ok? Should I use 22 gauge instead? Why?

2. How do I incorporate the shielding into the guitar wiring? Do I tie the negative and shield together at each side of the connection? For example on the pickup, there is a positive and negative lug. What do I do with the ground?

3. On the volume knob, I've seen 2 different recommendations on the intertubes. One is to have the pot adjust the positive from the pickup to the output and to wire the negative to the back of the pot. Others have the wire from the back of the pot also connect to the other poll of the pot. Any recommendations? And what do I do with the shield wire -- join the negative and shield wire at the back of the pot?

4. How about at the jack? I assume that I tie the negative and ground here at least.

Thanks for any feedback.

Answer 1

Normally all of the following are earthed (soldered to the casing of the volume pot)

• The outer ring of the jack socket (that's your main earth to the amplifier)
• The strings (via a wire to the tailpiece or bridge) - this usually reduces interference picked up by the strings
• The anti-clockwise tab of the volume pot (this little wire is essential for the volume control to work properly, so the pickup signal at the other end is "relative" to ground)
• The negative end of the pickup coil
• Screening wire/connection from the pickup, if there is one

Dodgy earths are, I would guess, the number one cause of electrical problems :)

Answer 2

Thanks much to @Andy for his answer. I thought I'd add my specific experience here for posterity.

• The thumb pot doesn't have a casing so I wired the shield wire to the "anti-clockwise tab" on the pot and wrapped it around one of the mounting screws before joining it to the negative wire.
• I tried not joining the negative to the shield at the pot and this created a lot of hum.
• I joined the shield and negative at the jack as well.
• I ended up not joining the shield and negative at the pickup but I tested both and there seemed to be no difference.
• The 18 gauge shielded wire seemed to work really well. The wire shield made an immediate difference on reducing the hum.
• I can't evaluate the stranded versus solid core although I know that stranded cable is at least a lot more flexible so maneuvering the wire was certainly easier.

I got the wire at Lowes in their pay-by-foot wire section. It was something like US$0.17/foot so I paid something like US$2 for 10 feet. I would twist the ground wire up and soldier it up to form a solid wire which allowed me to control it better. Here's an approximate picture of the wire I used.