The blue wire on a fuel pump is the power supply line, which provides electricity to the entire fuel pump assembly. This wire typically runs from the battery of your vehicle and supplies constant current to all components of the fuel system including the pump itself. The blue wire must be connected securely in order for the pump to receive electricity, otherwise it won’t be able to provide enough pressure or volume to pressurize and move gasoline through your car's engine. When replacing a fuel pump, make sure that you reconnect any disconnected wires correctly, especially if one has been removed during repair work. If not done properly, this can lead to costly repairs down the line due to lack of proper power supply. Additionally, having an understanding of how each component works together helps ensure everything runs smoothly and securely when making necessary repairs or replacements.