This harness connects to the factory wiring behind the radio.
The main harness above has the electronics to do steering wheel controls but this wire will tell it what radio you are installing. Since it is radio specific it is sold separately. If we do not have one for your brand radio use the universal one.
The harness above has an ISO connector on the radio side. This will plug into some radios. Check the google sheet on this products page to see if your radio will connect directly of of you will need to buy a converter to do a plug and play free installation.
Use the list below to figure out which one you need.
These tools come in handy when removing the cars interior trim.