I bought a new auto dimming mirror with Homelink (garage door opener) and compass to replace the auto dimming mirror which came with my 2018 EX. It was for a 2012-2015 RIO. I was hoping for plug and play since I already had 12V at the mirror, but no such luck.
The instructions indicated that I needed dc ground, 12V constant and 12V switched. I assumed the 12V constant was to use Homelink when the vehicle isn't running. The jack on the mirror and the plug from the vehicle were different, and the mounting bracket style was also different. I needed to swap wires and mounting brackets to get the OEM look and also to not rewire the vehicle.
I was able to open both mirrors to swap the brackets and redo the electrical wiring without too much trouble. I found out a bit of the hard way that there is only 12V switched. I made an assumption after finding the ground and 12V switched, that the remaining 2 wires needed to be connected. I was wrong. When I backed out of the driveway, I had trouble getting the vehicle out of reverse and it threw a transmission warning and engine light. I did more research and found out that the last line was the reverse signal for the mirror to, I assume, turn off the auto dimming when in reverse. Turns out the vehicle did not supply a constant 12V to the mirror, only switched from the ignition. I disconnected the reverse line from the mirror and put the switched 12V across both the constant and switched inputs leaving the reverse line disconnected.
I'm sure that one of the lines in the mirror will work with the reverse switch, but I'm fine with it as is. The garage door opener only works when the ignition is on.
I supposed to know better, but I was rushing. Now I just need to get the engine light and error code taken care of.