Need help - Navigation head unit upgrade in 2015 Prius C-2

Bought a navigation head unit that was meant for 2012-14 Prius C-3 to install in my 2015 Prius C-2. Although the nav stereo unit was not an exact fit with a small gap all around the frame, it sat well enough to be mounted. The problem I have a an excess wire plug from the 2015 Prius C-2 harness that does not fit on to the back of the replaced nav unit as shown in the pic. There is no such socket for the plug on the nav head unit.

There are 4 wires on this surplus plug and I don't know what they are for. Does anyone has any clue? Appreciate any advise. Thanks.