1dmurrray

While looking for a good garage door opening solution for my MY01 996 C4, I came across some posts referring to the Gentex auto-dimming mirror with Homelink. Some posts suggested that there was a VW/Audi adapter that would allow this universal fit mirror to be installed on a 996 windshield. Other posts suggested that it was easy to tap into the existing dome light and sunroof switch wiring. So I decided to give it a go. It was a relatively easy install, and one of my best mods yet. Step 1: I purchased the Gentex GENK40A Auto-Dimming Mirror with Homelink on Amazon (American Security Company) for $249. My kit came with a VW/Audi adapter and a free wire cover. Here is the mirror, the piece of the wiring harness that I used (it came with a full, route to fuse box wiring), and the wedge adapter. Here is a close-up of the adapter. Here is the wire cover. Step 2: Remove the old school mirror by rotating the base 90 degrees counter-clockwise. I put masking tape around the base and used channel locks and a firm grip to rotate the base 45 degrees. I continued rotating the base by hand another 45 degrees until it released. Be careful as you don’t want to break the windshield -- been there, done that on a wiper blade DIY, oops! Step 3: Slide the adapter onto the windshield button cam and secure with hex key set screw. Note that my adapter did not fit out of the box. I used a small file to remove material around the inside of the adaptor until it fit snugly around the button cam. Since the adapter is aluminum, this was easy work for a steel file. I also primed and painted my adapter matte black to make it more inconspicuous. Step 4: Plug the wiring harness into the rear of the mirror, and remove the large red harness at the other end. The color coding for the wires is as follows: (1) Red = switched power; (2) Yellow = un-switched power; (3) Black = ground; and (4) the two Green wires are not used for this mirror (they are used for other Gentex mirrors with temperature displays). Step 5: Mark the outer wire casing so that you can split it for purposes of routing the wires through the mirror base. Don’t forget to leave some slack for mirror adjustment. Step 6: Slide the mirror base over the adaptor. Tighten the mirror base set screw with a T20 Torx driver. Step 7: Now it’s time to remove the dome light / sunroof switch housing. First, remove the two black alien eyes with a plastic trim tool. Next, remove the two screws underneath the alien eyes. Then, carefully pull the end closest to the sunroof away from the headliner until the rear tabs release. To fully release the housing push it towards the windshield so the front tabs release from the mounting edge. You’ll understand when you are in there. Step 8: Identify the existing wires that you need to tap into. After testing with a test light, I used the following wires: (1) the Red/Green wire with black spots going to the sunroof switch for switched power; (2) the Red/Black wire going to the dome light circuit board for un-switched power; and the Brown wire going to the dome light circuit board for ground. Step 9: Install the wire cover by clipping it into the top of the mirror base, and route the wires from the mirror through the cover and into the dome light housing. Note the wire cover that came with my kit was way too long, so I cut it down to size. I also made a channel out of mine to cover the wire on the inside. The inside cover was cut a little shorter than the outside piece to make it easy to route the wires. The dome housing will fit over the wire cover, so thankfully there is no need to cut a whole in the housing. To make the install look cleaner from the outside, I intend to go back and use a thin strip of black film on the inside of the windshield to better hide the wire cover from the outside. You might want to try this now. Step 10: Now it’s time to make the connections. I used 22-18 gauge splice tap connectors. The connections are as follows: (1) Red to Red/Green with black spots; (2) Yellow to Red/Black; and (3) Black to Brown. I wrapped up the unused green wires with electric tape. Step 11: Reinstall the dome light / sunroof switch housing by: (1) pulling the front tabs onto the mounting edge; (2) snapping the rear tabs back into the headliner (you may need to move the wires around a bit to get a good fit); (3) replacing the screws under the alien eyes; and (4) replacing the alien eyes. Step 12: Test the install. The Homelink buttons should work when the ignition is off. Press each and you should see a red light come on. With the ignition off, the anti-dimming feature should be off. If you press the 1 button, nothing should happen. With the ignition on, you should see a green light indicating that the anti-dimming feature is on. You may need to press the 1 button the first time. It should go on and off with the ignition after that. You can verify that it is working by covering the sensor on the back of the mirror and shining a light on the sensor on the front of the mirror. I found that the mirror works really well in real life conditions. Step 13: Program the Homelink buttons with the included instructions. Step 14: Congratulations, you are done.