It will only have one output from the LNB assembly. You'll need to remove the assembly to tell for sure. Don't just rely on the fact that it has one cable connected.
What receivers do you have? If one is a dual tuner with only one cable connected and you are able to tune with both tuners, then it is also a good bet you have SWM.
If you have 2 receivers, both dual tuner, (me) you will not have to add additional wirings. One wire will go into each receiver, directly from the sat antenna.