You need shielding tape underneath the pickguard too. put the pickguard back on and make sure you have a little bit of the shielding from the control cavity running from the cavity to the top of the bass, so it can contact the pickguard. I usually place a small tab-like piece where a screw hole is so the screw can ensure they stay in contact.
You've gotten the conectivity, if I'm reading you right , so put the guard back on and the humming should go away. What you are trying to do is for a "box" or cage around the cavity.
edit: if you have the shielding tape underneath the pickguard it should go away, to be clearer.
Just wanted to update and thank everyone for the help in getting rid of the bridge ground issue.
It turns out that the original bridge has some "dead spots" in it. I can connect both leads of a meter and check the impedance with sporadic results.
I bought a new standard Gotoh bridge that, once installed, cured the ground buzz issue.
The best thing about this whole ordeal is that I got one of my favorite passive US Peaveys back in action. I love the neck on this '94 Forum, and the custom P/J pickups are great.
Thanks again.
