See what color wires go to the resistor in the in-tank fuel sender. There should be two wires going to the sender. You need to find which ones go there so you can wire one side to ground and the other to the gauge. It will also help you to measure the resistance of the sender while you have it out. Measure the resistance with the float all the way up and then all the way down. According to the IQUUS manual it should be 90 ohms.