The Gibson G3 bass wiring is actually quite simple. The G3 wiring schematic is not always easy to follow if you are not an engineer, but the actual connections are easy to decipher from these photographs.
The components shown are as follows. Pickups: three single coil G3 bass pickups, part numbers 13101 (front), 13102 (middle), 13103 (back) - see G3 parts lists.
Potentiometers: The G3 uses two different pots: the volume control is a 300k linear, part number 70031. The tone control is part 70033, which is a 100k audio pot. 1980s G3s may well have different part numbers and/or values.
Other: three way switch (part 19351) and input jack (part 70251).
Controls are scratchplate mounted, meaning they could be assembled remotely from the body/neck. This is a cheaper and more efficient means of production, but makes for more difficult maintenance later on.
G3 pickups are spring mounted to the scratchplate with three screws in a triangular arrangement, allowing easy height and tilt adjustment. Note that the three pickups have different colour wires coming from them: orange and black from the front pickup, two orange from the middle and orange and red from the bridge.
The Gibson G3 bass has just a master volume and tone control, and a simple three-way switch.
What would be the impact of using just two 500k pots please? Is it ok, or will it change the sound of the bass. What about a 500k instead of the 300k but still the 100k tone pot. These odd value pots are not easy to find
It is okay, you'll just have a brighter tonal range. Since these are single coils, i'd go 250K for the tone instead just to bring the headroom up a bit more. You can use any value really for Volume, to my ears it doesn't have much effect.
Can you tell me please, are all G3 basses wired the same. Were the black pickup version and see through pickup versions identical in circuitry? thanks
All identical - only the cover had changed. Circuitry is the same