Depends on the year. My 03 it is on the drivers side low in the kick panel. Black wire, pink stripe. Some trucks have it on the passenger side, same color.
You could have tried to S E A R C H
It works nicely.
I have had my f90BT for about a month and have had no problems at all. I love this thing. Putting in the back up camera so I can back right up to all the trailers I pull tomorrow. I cannot complain about it at all.