When replacing your factory radio with an after-market car stereo, the AWH190 (EWH1010 / 70-9003) wire harness is a must for a quick and clean installation. It eliminates cutting your OE radio plug. After connecting it, your install is simple as the wires will color-match and easily connect to the after-market stereo. Without the AWH190 (EWH1010 / 70-9003), you would have to cut the OE radio plug and manually test each wire to connect to your after-market receiver.
In addition, because you do not have to cut your OE radio plug off, the EWH-1010 allows you to reinstall your factory receiver if necessary. A great example is if you sold your car, but wanted to keep your after-market radio and re-install your factory stereo receiver.