My Watts Up meter is connected in series. Both the positive and negative leads are wired through. The positive lead feeds from my battery, through a 100A contactor, then a circuit breaker, through the meter and into the controller. The negative lead feeds directly from the battery through the meter and into the controller.
You can, and I'm planning on, wiring just the negative lead through the meter and running a small gage power wire to the source + connection, the load + connection would not be required. This "remote" configuration seems a bit safer as the meter is right there between my hands and face. You can see the different connection diagrams from my link above.
Andy