Footswitch controlled Pick Up selector
Ok Here is the basic quick and simple method of allowing pick up selection from a 2 button footswitch.
Advantages requires minimal modification to the guitar, ie no extra holes to drill only alteration to the existing wiring and uses components and swiches which are readily available.
Disatvantages guitar always needs to be plugged into the footswitch it cannot be used without, the extra length of the cabling could potentially alter guitar tone.
Typical standard pickup selection (3 way toggle ie les paul)

Basically all you need to do is disconnect the feed from the vulume pot of each pick up to the switch and connect them and the earth to a stereo jack socket instead of the normal mono guitar jack

The final part is to modify a typical standard 2 button footswitch (the type you often get with amps to enable channel switching you need a stereo jack socket and a mono jack socket.

Connect the guitar to the footswitch with a stereo cable, then run a std instrument cable from the footswitch to the guitar amp
one switch will turn on/off the Bridge pick up , the other will turn on/off the neck pickup. Turning both on will give you both pickups (the centre position of the original guitar switch.
Note I cannot comment on how much little the extra cabling will affect the guitar tone as it will depend on the length of the stereo cable you use but it will work. If you are really concerned about the effect the alterations may have on the guitar tone there are otherways of achieving the same as the above without the possible tone altering side effects but these are all a little bit more complex or require a bit more modification of the guitar. If you want more info on those just ask
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