The 3-way switch is certainly a good suspect, worth getting some switch cleaner and squirting it in there to see if helps. But without using a multimeter to check continuity, you'll never know for sure as the cleaner may make no difference.
Ozo - worth a photo of the wiring - some of the eagle eyed characters on the forum have picked issues from the photos. Often a small issue with the wiring (often grounding) can have bizarre impacts on the sound.
It's an ES style, Brendan, so not easy to photo without taking it all out of the body. But that's probably worth doing as getting the wiring harness into the body can cause a lot of wiring problems and broken wires.
If there's a Jaycar Electronics shop near where you live, next chance you get pop in and buy yourself a can of this stuff, it's a specially formulated electronic cleaning-solvent, I use it all the time on pots and switches, does a pretty good job:
Here's an example of a cheap digital multimeter that you can buy from Jaycar Electronics, catalogue number is QM 1517:
It features a continuity test function that produces a beeping sound if there's continuity, pretty useful to have.
Last edited by DrNomis_44; 15-01-2018 at 08:23 PM.
On my pb bass there are 2 sets of vol and tone controls. There is an issue with the wiring schedule in so much as if you set either vol control to 0 it earths the o/p for both pups. Alternatively you may suffer an intermittent problem like I had- found the issue eventually, hadn’t soldered the output pole of the 3 way switch do-oh