OK.. I just did this a few days ago on my 04.
You accept full responsibility for your own actions. If you are not familiar with basic electric circuits and splicing wires, GET SOMEONE TO HELP YOU!
1. Open sunglass storage compartment and remove one Phillips screw.
2. Firmly grip the edges of the overhead light/sunroof control assembly amd pull down. You will need to do this very firmly but carefully. The unit is very tightly secured into four self locking clips, but it will come down with persistence.
3. Remove both wiring harness connectors that feed power etc to the interior light and also the sun roof controls. put the light unit aside.
4. Above the mirror is a small telescoping channel against the glass. Pull this down and put aside.
5. Unplug the mirror connector from the back of the mirror. Pull the mirror supply wire and plug back through into the hole where the light was removed from.
6. Using a razor knife of a small pair of pointed nail scissors, carefully cut the outter insulation sleeve for about two inches. Do this close to the head liner (furthest away from the plug end) Inside will be three wires. Black, Orange, and Black with red stripe.
7. Splice your detector wires to the black (negative) and Orange (Positive), and tape insulate each wire completely. Put the splices back into the sleeve, and apply more tape to close the "wound".
8. Feed the mirror wiring back to the mirror, and the detector wire to the detector, following the same original routing. Reinstall the channel, and mount your detector.
9. Reconnect the wiring connectors to the interior light unit. Reinstall the unit by carefully aligning the clips, and reinstall the phillips screw.
10. The fuse will be OK as the detector draws very little power.

Good luck.

 

I ran mine tucked under the headliner along the roof over to the a-pillar, then under the a-pillar down to the dash and then to a fuse in the fuse panel which comes on with the key.