In regard to the soldering I have a 4 wire.
yes
4 covered wires (red, white, gren and black and a bare uncovered wire)
On the diagram supplied with the pickups it shows the actual main black wire coming out of the pickup itself soldered to the back of the volume pot...wouldn't this melt the plastic all around the wires? Doesn't seem right.
No - not that wire - you are soldering the thin black wire to the back of the pot as well as the bare wire.
the green and white wires are to be soldered together and taped or heatshrunk out of harms way
this is the series connection.
Should I wire the red wire to the tag on the volume pot and the black and uncovered clear wire to the back of the volume pot as an earth?
Yes - spot on correct
Why would the diagram show the main thick wire soldered to the pot or is it different for braided 2 wire?
on a braided 2 wire the outside of the main wire is the earth connection for the pickup - so that outer casing will get soldered, whilst on a 4 con wire the outer casing is a plastic/pvc sleeve and wont solder , so you use the bare wire within and one of the four covered wires as well to be connected to earth
Many thanks guys! So excited to get these wired in!!
Good luck with the soldering