I think this thing has (temporarily) beaten me.
Today I pulled it all apart again and carefully resoldered.
No change.
I removed the tone pots from the circuit, still nothing abut loud hum and nothing from the pickups.
I removed the neck pickup and went straight from bridge pickup through the pot to the output, no change.
The only thing I haven't tried at this point it pickups directly to jack.
I used a better (hotter and finer) soldering iron and finer solder this time and I cleaned up all the joins and re-did clean.
I also used new wire for a couple of them.

Luckily I should be getting the complete harness next week