For the AN650, open the front locking glove compartment.
On the left side of its inside door grommet a tab is visible that when you pull it, it will open the Maintenance Lid that will hinge from its left side. Inside is the fuse box (left) and side-stand relay (right). The fuse block wires can accomodate your custom power bus for the XM.
I recommend tapping DC from the 40 amp main fuse block terminals. Wire a second fuse inline with the tapped positive (+) line just for the XM if it does not already come with a fuse.
Use heat shrink tubing on the splices, not electrical tape. If your attempts at heat shrinking the exposed splices still shows exposure, use GE Silicone Seal to gloop the wires and soldered splices into a solid insulated form.
If you're willing to tap the cigarette lighter receptacle for XM power, the front panel needs to come off. The front panel is all three glove compartments.
First you'll need to to remove the Handlebar Rear and Handlebar Front covers.
Look at a service manual first (Page 9*8).
The service manual doesn't explain how to get the Front cover off once the retainers are pulled out but remember that the Front cover is hooked onto the handlebars center in two places and it needs a strong upward motion to get it free.
The three screws on each side of the glove compartment (Front Panel) are color coordinated and need to be placed exactly where they came out upon re-assembly. Use a number #2 Phillips or #2 Reed Prince on these screws so they won't mar. Also the book doesn't mention it but once you get all the screws out of the Front panel, there are retainer clips on the inside center of it (left of ignition key hole). By pulling at that point and holding onto the now exposed rear, the whole thing will come flying off. Be careful not to lose the two retained metal nuts that mate the screws from the Front Panel to the lower plastic body sides. They can fall into this cavity and they are $1.80 a piece.
Look at a service manual first (Page 9*8).
The Mickey Mouse wire gauge size that's feeding the receptacle 12 volts will make you agree: Fuse the XM circuit separately.
And by the looks of Suzuki's wiring into the 12 volt receptacle, We'll never power a 12volt heater or small fridge with it either, however it'll make a great tap for the little XM Radio.
Look at the service manual Page 9*11.
They call it a Front Leg Shield Cover. It's under the 'S' suzuki logo and it has the intake air vent that is all black plastic. By pulling it off, you'll notice that there is enough plastic cavity area to mount the antenna inside of this cover through the now exposed Front Panel and under or on top of the speedometer (Combination Meter - Page 9*22).
Exposing the XM front panel, antenna or cable invites vandals.