Sitting here for 2 hours and couldn't find exactly an answer. I am swapping a 1999 civic motor into a 1998 body and as you know the OBD2b wiring harness is 3 plugs going into the ecu with the forth plug coming from the cabin harness and the OBD2a has all 4 plugs. I have both complete vehicles so what is the easiest way to complete the project? I think I am to run the 1999 ecu with the motor but how do I get that 4th plug wired in, I see Rywire has an adapter kit available. I'm a old guy just fixing my commuter!

 

use your 98 harness. swap the distributor from the 98 onto the 99 motor. use the 98 ecu. the 99 ecu will throw a code for fuel tank pressure sensor. plug the air injection hole on the intake manifold.