im new to the whole hybrid thing so expect me to say some stupid stuff . which 2 of the three (engine, ecu, chassis) does the conversion harness effect? the reason i ask is because im planning on putting an obd2 b18c into an obd0 crx si or hf with an obd1 p72 ecu. would it be simpler to buy an obd2 ecu? btw, would it be an obd2 -> obd0 harness or an obd0 -> obd2 harness?

 

To understand the OBDx to OBDx is like this: The car you will be working with is a CRX, which is OBD0. The motor you want to install is an OBD2 B18C but you want to use an OBD1 ECU. What you would want to buy is an OBD0 to OBD1 ECU adapter harness. The only way you would want an OBD0 to OBD2 harness is if you plan to use an OBD2 ECU.
The conversion harness basically changes your chassis ECU plugs into whatever style ECU plugs you are planning to use. The OBD of the motor is not as important as matching the OBD of the ECU to the fuel injection components and distributor for the most part.