Photos of each part of the loom would help, from output jack to each pot and switch etc. Clear and close-up, if possible. Often times it’s something that only other eyes can see.

Common on things to check:
Reversed output jack connections.
Bad ground lug connection on a volume pot.
Stray strand of wire from a ‘hot’ brushing a ground point.

Does it happen in all switch positions, are your getting sound from the pickups with a tap test, does either volume affect the hum? Sometimes disconnecting each pickup from the switch one at a time can help to narrow down where the issue is occurring.