With the truck idling, and a test light in hand, open the lid on your seven pin connector on the rear of your truck. Attach your ground to something absolutely sure to be a good ground and touch the probe to number 4 pin which is the one in about the 10:30 position. That is your wire which charges the battery in the trailer. If it's hot then you should be in business as far as your TV goes. If it isn't hot then take the advice given above and go from there.
