Longtube headers have the oxygen sensor bungs located further back than OEM stock exhaust systems, which prevents the factory wiring harness from reaching the oxygen sensors. The BBK O2 Sensor Extension corrects this problem quickly, easily and economically, using the stock OEM connectors. That way, they simply plug into the existing connectors. The BBK O2 Sensor Extension is an especially necessary component drivers looking to change out their midpipe and full length header applications on the 2004 Mustang. The BBK O2 Sensor Extension harness extends all the way to your 02 sensors, which enables them to actually be connected to the harnesses that transmits the data to the vehicle's ECU regarding the status of the vehicle's systems. This will eliminate the annoying illumination of your MIL light, and will work for all Mustangs built between 1986 and 2004. BBK has manufacturing and design facilities located in Corona and Temecula, California just outside the LA and San Diego Metro areas, where thousands of high-performance products are turned out each year. BBK Performance products have become well known since 1988, and have been given high marks by New Hot Rod, Fords Magazine, Muscle Mustangs & Fast Fords and other industry publications. Auto parts buyers always deserve high quality help when they buy good quality parts for a car or truck. Thus, we built a round-the-clock support call desk to support you with your questions. Everyone hates paying for shipping, so there is always free shipping for all orders at least $50. If you find a better price, tell us - we will beat any legitimate auto part price.