Can you get the on screen directions on your TV from the Furrion if you hit setup?
If not you may need to check the HDMI connections at the TV and on the back of the Furrion. The head unit is easy to remove. Pop the plastic trim piece from the top and the bottom of the stereo which will expose 4 screws. Take those out and the unit will slide right out. There’s both HDMI in and out ports on the rear of the unit. Make sure the cable to the TV is connected to the out port.