I just replaced the neck pickup on my Fender JP-90 (a PJ bass) with a Fender Pure Vintage ‘63 Precision Bass pickup. The wire on the original pickup had broken off at the base; someone had been inside before I bought the bass, and the wire must have been barely hanging on. I’m amazed at how thin the original wires are. Individually each pickup is nice and loud. (Surprisingly for the same volume, the neck pickup is closer to the strings than the bridge pickup.) However, with both pickups selected the sound is weak and thin, unlike before the swap. We wired the white lead to the switch as before and as specified in the instructions that came with the pickup. Both white wires are at the switch, and both black wires are grounded. Could it be that the the pickups are now out of phase, like when speakers are out of phase? Any other ideas? I will take it back in on Monday to experiment with with reversing the wires, but first I wanted to appeal to the group mind.