What Purpose Does This Resistor Serve?

Steve, my Fender official looking Jaguar wiring diagram has a similar looking resistor across the low cutout slide switch (the one farthest to the right in your diagram) It shows as 120K on my diagram. My diagram is for a HH Jag and does not show the value of the master tone pot - I think we probably used 500K but frankly don't remember.

Just guessing from its location across the wiper of the tone pot I'm going to say that it changes the taper of the pot - remember that resistors in parallel add the reciprocals of their values.

 

It's odd. I was thinking it would change the taper and set a minimum value to the tone resistance, but the way this is wired, it's not clear what the benefit is. I'd note the 'original' Jaguar wiring diagrams I can find do not show the 56k resistor.

Here's a plot of frequency response (magnitude only) with and without the 56kohm resistor. (Edit, updated for similar sweep on the pot, 0.001 to 0.95.)

 

That resistor would make the sound darker in that position I believe. That or change the taper. Normally the pot resistance makes it brighter.

 

This old thread of mine got a final reply, which I don't recall reading before. Sounds like the answer.

https://www.tdpri.com/threads/johnny-marr-jag-tone-circuit.910573/page-2#post-9967493

In short, to make the tone control still work right when the bright cap is engaged.

Also note, people chimed in there, or somewhere back then, and informed us that every Jag anyone could ever recall, also had that same resistor.