You can find this product under Exact Fit Switchback LED Daytime Running Lights/Turn Signal Lights For 2014-up Mazda 3 (70-781).
Step 1: Remove several screws and clips so you can open the bumper. There is one clip at the top and two clips at the bottom.
Step 2: After you remove the clips, open the bumper.
Step 3: This is how the turn signal lamps look like from the back. There are four screws you need to remove. Two screws are circled, and the other two are pointed by the arrow.
Step 4: Put back the LED. When you install, you will see two sets of wires. Plug the three-color wire back to the module box and the yellow-color wire to the existing stock turn signal adapters. Twist to lock it back to the opening of the daytime running light. You will need to match the gaps to the size of the clips to properly insert.
When you put back the stock turn signal light adapter you may encounter some resistance. All you need to do it push it a little or trim the opening.
Step 5: Put back the LED daytime running lights.
Step 6: Repeat on the other side. Connect both of the LED daytime running light lamps to the module box. Draw the wires to the driver side battery + fuse box location. Connect the red wire to the ACC (the location is circled) and connect the black wire to battery negative or ground.
Step 7: Close the fuse box cover.
Test to make sure everything works. If the turn signal function does not work, flip the adapter around 180 degrees.
When successful, put back the bumper, screws, and clips. Enjoy your LED daytime running lights and turn signal lights!
Note: When you quickly switch turn signals from driver to passenger or vice versa, you will briefly notice the turn signal flash amber, then white for a split second, and back to amber again. (However nobody switches that fast from one side to another anyway)