I also ran into that problem with the harness. I got my extention from Downs and man that thing is long!! Mine was a universal extention so you have to line up the 02 sensor and the harnes and shave off the guides on the extetion that are not needed. They are the pertruding plastic guide thingies for lack of a more technical term. Ones these are shaved off simply plug the extention in. I would not recommend using any after market o2 sensors...I tried those and they suck!! Got Check engine codes after 2 months. Switched to Motorcraft and no problems. Only use Motorcaraft and make shure they are calibrated for your car. Calibration code should be on your door jam drivers side.
93 Hatch, R331 - TFS "Street Heat" Aluminum Heads - S-Trim 15lbs of Boost - Holley Systemax Intake - Anderson Power Pipe - Aeromotive Fuel system - 72 lb injectors - Accel DFI Gen VII - Snow Performance Boost Cooler - 661 RWHP Full interior - 10.70's @ 135 w/ traction issues!!