Speedo reads 20 sitting still and fuel gauge moves toward e when I turn lights on.

[dhughins]

I recently got truck and the electrical part is all hacked up. The speedo reads 20 and goes up when I drive. I'm not sure if it's just 20 off all the time or worse. When I turn on the lights the fuel gauge starts going to e until it's all the way left. Turn off lights and it goes back to where it was. Any of y'all seen this before. I wanna be able to drive truck so I'm not able to completely rewire it. None of the air or heat stuff has electricity to it.