Just listen to hum. With the humbalance trimpots turned all the way off, orient the bass physically in space to where the hum is the loudest. Now, listening to one pickup at a time, see that the hum decreases and then increases when adjusting the trimpot through the null (about halfway up). If both pickups null when listened to individually, then that means that all 3 coils (neck, hx, and bridge) have the same polarity.
If they do, try the
humcancelling procedure.
If you want to check the resistance, all 3 pickups should have approximately the same DC resistance. If you make these measurements, let me know and we can comment if they are close enough.
Magnetic polarity can be confirmed by placing the faces of the neck and bridge pickups together, they should repel eachother.
Turn humcanceller all the way off (turn down both humbalance trimpots) and listen to see if the the pickups have approx the same volume, and that they don't sound out of phase with the humcanceller turned off.
Let me know what you find out with all this testing.