Just added a Homelink 3-button transmitter to the C5 as part of a sunvisor replacement. Obtained from Eckler's $230 (noting that the basic sunvisor w/o the Homelink is $100). The installation is simple once one knows how to remove the visor from the car, all of which is detailed in the C5 Service Manual. The trick is knowing that inserting a tool in the sunvisor bezel slot (the slot doesn’t provide access to anything) and using the horizontal rotation of the sunvisor elbow against the 'tool' in the slot, will rotate the bezel out of its holder and allow one to access to the power wires for the vanity lights and Homelink transmitter. See this link for the service manual applicable steps:

https://picasaweb.google.com/krgoodw...eat=directlink

I see that the Tips section has the same instructions (complete) for the "Sunshade Replacement Removal Procedure"

The instructions provided by Eckler make a point of having you check the DC polarity of the power leads to the sunvisor. They are not kidding, my red wire was the negative lead and the white wire was the positive (maybe some power engineer wired the car for it sure wasn’t an electronic engineer). The Homelink instructions were very detailed – no problems getting my two garage door openers to work. The other transmitters in the other cars were not impacted, they all work as expected.