This is for a 2014 Elantra Limited w Tech and worked for me. Car only has a Blue Link rear view mirror with no apparent Homelink functionality (I've had Homelink for years so can't live without it.) I searched around but found no useful info other than some Veloster upgrade. Buy a Hyundai OEM Blue Link/Homelink mirror kit online that apparently is for a Sonata but will work for Elantra (you must use Hyundai Genuine Kit/Part #3Q062-ADU00)...See below Pic #1. If the kit is new, it should provide the mirror with both Blue Link and Homelink buttons (and auto dim and compass), wiring harness, t-tap wire connectors, foam tape, and instructions. Follow these Hyundai instructions but here it is in brief:

Remove negative battery terminal. Remove stock Blue Link mirror and unplug factory wiring harness. Put in new mirror and plug wiring harness into new mirror and factory plug. Remove overhead sunglasses holder/maplight trim (open sunglasses holder and remove two black screws, then carefully pop out remaining trim around headliner with nylon pry tool)....See Pic below #2. This trim piece will now be hanging by the maplight and sunroof wiring harnesses (note: the maplight wiring harness is a four white plastic plug deal on the left side that you will need to tap into)...See Pic below #3.

The new mirror kit wiring harness has two loose wires: (1) Black (constant hot) and (2) Black w Red stripe (switched hot). As I said just above the factory maplight wiring harness is a four wire white plastic plug deal on the left side of the hanging sunglasses/maplight trim piece you removed and the Red wire on this factory maplight plug is your "constant hot". Using the new mirror kit t-taps, connect the new kit wiring harness loose Black wire to this maplight wiring harness Red wire...See below Pic #4. Next...The factory mirror wiring harness that you unplugged from the factory mirror also has a Red wire and this is your "switched hot". Using new mirror kit t-taps, connect the new kit wiring harness loose Black w Red stripe wire to this Red wire...See below Pic #5.

Re-connect battery negative and test your new mirror. Blue Link and Homelink buttons should work...Auto Dim/compass should work (note power button in center of new mirror for these functions)...new mirror kit instructions explain how to set up Homelink with your garage door remotes and get the Compass accurate by driving in a few circles. Once you've got all the buttons working, follow new mirror kit instructions to snug up all wiring with included foam tape and re-install sunglasses holder/maplight trim piece in reverse of removal above...again, use the right tools and be careful with your headliner. The job is doable with patience and being careful...and results with a super functional mirror for your Elantra...again, See below Pic #1. Good luck!