It's been a long time but here goes, #1.Resistance in series add's up for the total amount of resistance. This would add to resistance and gauge would stay at the top longer. #2. Resistance in parallel by ohms law is R1 R1 10 x 10 = 100 example: R = --------------- so R = ---------------- ----- = 5 R1 + R1 10 + 10 = 20 Resistors in parallel become lesser the value of one. In looking at the diagram, The sending unit is a variable resistor with x amount of resistance built into the resistance wire ( ohms.) By paralleling another resistor to the sending unit would lessen the ohms and change the reading to the gauge. As best I can tell and having my unit out, the light comes on because of a mechanical thing not because of resistance. In other words, when the slide goes down it shorts to ground and light comes on. Thats why the light doesn't come on gradually. Mine will come on and go off as the gas splashes around when at the bottom of the tank and when it get's so far down it stays on. I have driven 10+ miles with the light going on and off . I also know that when I get below a 1/4 tank I better fill up. I haven't had and old gauge to experiment with, but if anyone has a bad one I could verify quickly. My $0.02's worth John vin11004