I'm putting together a SG build and am considering wiring it differently.
Is it really necessary for the pickups to have separate tone knobs? I'm considering keeping the volume separate and having a master tone knob, leaving the 4th free for some onboard effects.
To do this, I believe I would connect the volume pots to the same spot on the tone pot, then wire the effects in just before the output jack.
Note that wiring both the volume pot outputs direct to a common tone pot as first suggested would result in the selector switch being bypassed with both pickups permanently on.
If you never use the tone pots you can omit them and use two pots for effects control. Or have a master volume and master tone plus two effects controls. Or one master volume and three effects controls. A master volume allows you to have this as the last control in the chain, so the effect always works at full signal strength, which will help with signal/noise ratio. But it will depend on the effect as to whether this is beneficial or not. If you had an overdrive, then you’d probably want to be able to vary the amount of signal fed into it to control break-up. But if say a chorus or delay, then volume can easily be put after it.
So have a think about what effect(s) you want and how you’d like them arranged with regards to signal flow. You can always squeeze in an extra pot, though you may have to rout out a separate battery compartment depending on the complexity/size of the FX electronics.