harnesses are illegal nationwide. the harness has to be DOT approved, and currently the only DOT approved harness is from Schroth. you are required by federal law to have DOT approved restraints in your vehicle. ive have friends given a no seatbelt ticket when wearing full 6 point harnesses instead of the factory seat belts.
also if you do install harnesses, install them properly. use a full FIA or NHRA approved roll cage with an integral harness bar, or else a purpose built harness bar. attach them to the floor properly. an improperly installed harness can actually cause more injury than a factory restraint system.