Loaded pickguard mod with Japanese Strat

I have a Japanese Fender Strat ST62 which I've had from about 1994. I've bought a Fender loaded pickguard for it, installed it following the instructions on the Fender website, but I've ended up with the shielding pane wire with nowhere to go on the ST62. Ive also replaced the output jack with a Pure Tone multi-contact jack whilst the bonnet was up.... The pickups all work when testing them but now I just have a horrible loud buzzing.

What could I have done wrong, or is this due to the shieding pane wire? What can I do to try and find the cause of the buzz?

Did you run a ground wire to the tremolo arm claw?
That would make a BIG difference.
It would make the guitar quiet down when you touch the strings.

Yes - I did that - I've soldered one of the black wires to the trem claw

If the guitar had no hum/buzz issues with the original parts and you correctly installed the new loaded pickguard then there is something amiss with it -- the new pickups, the new controls, and/or its wiring.