The way that pickup switch is grounded on one end makes me think the pickups were wired in series. The switch is probably an on-off-on and the 4th tab is just a ground connection. I don't have and can't find an actual Danelectro schematic, but it should be much like the Duo-sonic. Colors may, or may not, be different and you'll have to trace them out, but here's that wiring diagram. The pickups are in series and the switch shorts out one or the other, depending on switch position- or neither if in the middle.