Bill's old color wiring scheme had black and green wires coming from the north polarity coil and the south polarity coil had red and white leads. Bare wire was there to provide extra shield when connected to ground.
For wiring these humbuckers in series, black+bare wires connects to ground and red serves as pickup hot out.
Four wires enable series, parallel, phase switching and coil cuts.
Some models had twin wires - red(hot) and black(ground) - plus bare shield. These where/are not easily switchable. Three wires plus bare enables coil cuts and phase switching.
My guess is that a 70's/80's three lead pickup's white wire is the series connection. Black has to my knowlegde always been ground connection.
Check with a multimeter. Take an Ohms reading between black and red wires. This should be twice the reading between white and black wires and white and red wires.