If you have 12V coming out of the Winegard power supply but no 12V power at the head of the Winegard there are only 2 possible reasons. The most likely is that you have the wrong cable connected to the power supply and the second most likely is that you have a bad connection between the power supply and the Winegard. Depending upon how close to the TV tower you are located, you might be able to scan 15 channels with nothing but a coax connected to the TV.
If you have no 12V power in the coax at the head of the Winegard antenna, your antenna is not "working". It's not even in use.
You need to be able to trace each coax line and find the origin and termination point of each. If you do not have the tools to do so you can make one or you can take it to a dealer to trace down the correct cables and get them to their assigned locations.