Patrick Keane writes “Here’s how to add a homelink to your car: 1) Buy homelink visors from ebay as cheap as you can get them from any car you like. 2) Tear them apart, and remove the Homelink module. 3) Cut small opening in headliner / dash panel / or opt to rewire the buttons and creatively locate them. 4) Attach +12V (black) and GND (brown) wires to nearby power source (overhead lamp). 5) Train it using your garage door opener(s) (see homelink.com). 6) Admire your $25 (maybe less) homelink installation. 7) (optional) Deprogram your old battery powered garage door openers and sell them on ebay for a profit.” Link.