Help with high pass filter in bass guitar

Would anyone be able to show me how I could wire up a high pass filter into my current wiring?

You could just add a capacitor in series with the signal connection (green) from the volume pots to the output jack.
Add a pot or switch across the capacitor to bypass it or adjust the effect.

I'd start with a cap of the same value as on the tone control & see how that works? It will probably take a bit of experimentation to get the best sounding effect.

You could use a could use a couple of plugs or a plug and socket to initially experiment, with the capacitor in series with the signal wire & ground/screen linked through, external to the guitar, to work out the ideal value and control circuit, rather than keep re-modding the guitar itself?

(Or put it in a small box inline with a short cable for use when needed).

Hopefully im understanding correctly, is this what you mean?

Not quite; like this:

The metal case of the pot should be connected to the case of one of the other pots (or ground/screen), but all three terminals are signal connections and not grounded.

Youre amazing! Thank you so much for getting this to work for me.