I went to wire the thing up tonight.. and ran into more fun.
So apparently, its four wires + a grounded shield. I'd missed the yellow wire as it had ended an inch up inside the shielding instead of poking out the end.
Using alligator clips I've tried R+B and W+Y, R+W and Y+B, W+B and R+Y, on the hot and twisted together for each. No matter which combo of wires I've tried, the thing hums like mad as soon as I get a cable plugged in.
I've got the outer shielding stuff twisted up and on the ground lug and the ground wire from the bridge is coming in at 0ohms so that line is good.
On this drawing, the black wire would be the twisted shielding from inside.. Coax, right? That stuff is the ground?