Here's a detailed write-up I did a few years ago when I installed my compass (pricing and availability have obviously changed since then):

I ordered the compass module from GMPartsDirect for like $ 135.00, part # 1647056.

Remove the following:

• The black plastic shroud over the brake and gas pedals
• The center filler below steering column
• The floor seat belt trim
• All door edge carpet edging at the drivers door

I also pulled up the carpeting along that edge, exposing a black plastic raceway which is used for the factory wiring.

While you are under the steering column, drop the central power supply box from it's mount located over the gas pedal, which will bring down the wiring and connector for easier access.

Compass Pinning Info:

1. Data Line
2. Data Line
3. 7 Volt Power In
4. 7 Volt Isolated Ground

I used #14 THHN stranded wire for the installation, as I had it on hand in multiple colors and the stiffness and quality of the wire makes it easier and neater to work with and I taped the bundle together like once every foot with electrical tape.

I was unable to locate the proper connector, so I made individual crimp sleeves to attach each of the four wires to the appropriate connection pins on the compass.

The compass was mounted on the under the rear window shelf on the drivers' side using industrial heavy duty Velcro like the stuff they use for EZ-Pass toll transponders. Wires were easily fished thru from the trunk, without removing any of the rear shelf trim using a dry cleaning hanger as a snake. The raceway under the drivers' door opening is hinged to allow you to lay the new wiring in. I snaked the wires up thru the kick panel raceway and to the area below the steering column where the wiring splits off from each other.

The 2 data lines were routed to the ALDC connector located just above the emergency brake, connection easily made by removing the connector and using inline taps to the the data wires from behind the connector. The data lines are tan and are the top left 2 wires going into the rear of the connector (it doesn't appear to matter which wire goes to which in the data loop).

Power lines were routed up and over the steering column and to the hanging power supply. I unhooked the power supply connector (everything in the car goes dead when you do this). Looking at the power supply connector, there is a blue and a beige termination stay within the connector, you want the beige set, which is numbered. power to the unit goes into #16 and the isolated ground goes into #7. push the beige wire retainer back into the connector and reattach to the power supply.

Computer Programming Instructions (thanks to Sahein):

1. Get into diagnostic mode by pushing the climate control warm and off buttons simultaneously.
2. Select BCM then BCM override.
3. Select BS07.
4. Remember this displayed number so you can return the BCM programming to normal.
5. Push override up arrow until code 252 is displayed.
6. To permanently store the new option code: Press and simultaneously hold for more than 3 seconds the GAUGES and OPTIONS buttons surrounding the display.
7. Turn the key off and then back on.
8. Select the OPTIONS button surrounding the display.
9. compass should appear in the menu. All of the old options are still there but located under a different level.
10. Smile 

The compass screen comes up whether there is a compass attached to the car or not, so before you close everything up, go thru the calibration setup on the compass screen (this will involve driving the car in a circle), don't worry about directional accuracy for the moment, just make sure it changes direction when the car does. If the car asks you to point the car north after the circle, congratulations, it is working! hit return to see you compass in action. if the directions change with the orientation of the car you are good to go. Close up all that you have disassembled. Afterwords

I re-calibrated the compass with a hand held compass to ensure accuracy.