I just completed the installation of an OEM style garage door opener in my 2008 Passion Coupe. This remote is the familiar 3 button Homelink transmitter found in many vehicles, but NOT available as a factory option in our fortwos. While the ubiquitous visor clip-on works, it is truly inelegant and I wanted a built-in.
Be forewarned! This mod involves cutting holes in the overhead plastic trim. A mistake will cost you $80+ for a replacement part. Precision is not required, but disaster is always possible. You will also be working around wiring that could also be damaged by a drill bit or knife. Your mileage may vary; don't call me if you mess up!
Enough of the downers! Let's do it!
Step one is to acquire a remote transmitter. I'm sure you can buy a new one for some obscene price, but salvaged units are readily available on eBay. Just search for "custom homelink" and you should see a number of items that look like this
You will see three different types in a variety of colors. The "rolling code" models appear to be needed for newer garage door openers, so that should be your first choice. If you have successfully used a non-rolling code remote, you can save a few bucks. I believe the rolling code version will work with almost all openers. There is a third variation with a built in voice note recorder for the true geek! Prices range from around $12 to $40 with shipping. I succeeded in getting one for $18.50 delivered.
After you receive your remote, the first task should be to test it and get familiar with programming it. There are many websites with Homelink programming instructions, so just Google for it. You will have to rig up a temporary 12v power source -- I used a spare plug-in adapter and just twisted the wires. The Homelink's power connector is not labeled -- the negative connection is the wire closest to the center of the unit (on the left in the picture).
Once you're confident that the device works with your garage opener, it's time to hack it into the overhead trim. I mounted mine just below the courtesy light:
Power for the transmitter can be picked up from the courtesy light wiring. I used two press-on taps to make the connections.
The hardest part of the installation is the mechanical mounting of the transmitter. I spent a couple hours figuring out the exact location of the holes, and then a couple more hours carving them bigger with a knife until they were where they SHOULD be. I'm not showing details here -- I will be installing a remote into my wife's Cabrio and will take pictures during the installation process.
I had to make three tiny spacers to enable the buttons to function through the thick plastic of the Smart's trim. After searching through my junk boxes for suitable material, I ended up cutting 1/16" slices from the end of a plastic chopstick, and then using a dab of superglue to attach to the switches in the transmitter. The other challenge is getting the button housing to fasten securely to the transmitter through the trim. I'll document that also.
The final product is worth the effort. Start shopping for your transmitter and I'll continue the instructions as soon as my second unit arrives.