Fuel gauge wont stay still!!!!!

[Bartenfeld]

with all of the lights off and no turn signals blinking, my fuel gauge is fairly accurate. However, when I turn the head lighs on the gauge will drop almost half the span of the gauge.

I.E.- if is says the tank is full with the lighs off, when I turn the lighs on it will drop to half the half full mark.

Also, if I introduce the electrical current of the turn signal, it will then fall even more and jump back to the half-full mark corrisponding to the blinking of the turn signal. What is going on here???