The Orange/Blue wire is used to operate the fuel pump. When the Haltech ECU wants to operate the fuel pump it will close the fuel pump relay, which will supply the fuel pump with 12V from the Battery. It is important that the fuel pump is capable of the correct fuel pressure at full power, otherwise the engine could be damaged due to a lean fuel mixture. For example, a 500hp engine requires approximately 210lb/hr for a petrol engine. The fuel pump must always be mounted lower than the outlet of the fuel tank or surge tank. Ensure that all care is taken to keep fuel cool. A change in fuel temperature will change the air/fuel ratio because as fuel temperature increases its density decreases.