A 4-wire humbucker is like a pair of single-coil pickups monted on the same frame. Both ends of each coil are available for connection in any combination you want.

Check out the wiring diagrams shown for the humbuckers on the >DiMarzio< website for some ideas. If your pickup is made by a different company, the wire colours may be different, so you will need to visit their website to find out which wire goes where.