i hate to be 'that guy', but why would you want to go OBD2? its more hassle, more money, and harder to upgrade on (ok, well, marginally)...

if u have an OBD1 car (with harness), you will need to run, at most, 3 wires for it to work with a stock OBD1 ECU...

anywho, if u are re-using your EG OBD1 engine harness, and want to go with an OBD2 ECU, you will need "OBD1 to OBD2" conversion harness.