you can use either wiring harness because if he had a vtec model in the car already than it was set up for that motor, unless he had his harness altered and is keeping it with his motor. the only issue would be what ecu would you be using, if you use yours it has the IAB's already in it, if you use his, you will be without unless you use a new I/M, like i did. but you can use either harness