ok I hate to bring up really old posts but this needs to be updated.
First, the new Sirius Radio's have a voltage step down in the cig-lighter plug so they go from 12V down to 5.2V. If you try and use 12V the radio just will not turn on so you need the voltage thing. There are a couple ways you can do this.
1) Take the end of the lighter plug apart and wire it inline.
2) Install a female power adapter under the dash somewhere.
http://www.tss-radio.com/cigarette-lighter-hardwire-adapter-p-4057.html
3) buy a install kit like this one:
http://www.tss-radio.com/sirius-vehicle-power-hardwire-kit-p-4438.html
I chose to do number 2 since I already had a spare adapter to hardwire in. The added benefit of this is it also allows you to reuse your wiring for other accessories you may change to later. i.e. say Sirius merges with XM, you want a new radio, and find out they changed the voltage requirements yet again!
Here is a couple pictures of my install. The wiring harness is right under this bracket so I chose to use double sided tape versus screws for my mount. I could have moved it somewhere else, but this was really really easy and will be very quick to get to if it needs changed in the future since the center panel just pops down.
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I also chose to use this littlefuse mini add-a-circuit thing because it can be put in place of a current fuse and holds the current fuse plus the new fuse for the additional item. This allowed me to use the Radio fuse so my Sirius now comes on and off with the car ignition switch. It's like it built in and now my wife does not even have to turn it back on, the satellite radio is just on.
http://www.littelfuse.com/data/en/Data_Sheets/FHM02FHA02.pdf
The only thing in the instructions that can be a little confusing is the ground wire location. The ground is located behind the drivers side kick panel as shown:
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