young.till.i.die

i just picked up a sweet pre-owned 09 Mazda3 and have a question regarding the factory Sirius setup.

The car was advertised as having satellite radio but the SAT button does nothing. I now question if they meant "satellite ready" or if the actual module is installed. I pulled the HU and saw in addition to the main radio and display harnesses, there is a harness plugged into the satellite connection on the back of the HU. does this mean i have the sirius module installed somewhere in my car? the sat harness is all wired into the factory harness.

if factory installed, should i have one of the square magnetic sat antennas mounted somewhere on my car? ...because i don't. (at least not one visible).

i have a sirius aftermarket setup from my old jeep that i'll use if i don't have the factory module installed.

one more question - is there a reason why most aftermarket sirius install posts mention tapping into the cigarette lighter power wires rather than the head unit wires?