Today I completed a conversion harness from OBD2a to OBD2b for my 99 B18C ITR (P73 OBD2a) motor swap into my 1999 Civic EX (OBD2b). There were 4 wires I could not map between the diagrams for the OBD2a and 2b.

The three wires hanging back over the ECU:


The only thing missing is some marinara sauce... Chewy spaghetti!

(All terminal locations are OBD2a)
A25 White/Black VREF - Reference Voltage lead doesn't have a home on my OBD2b computer. Anyone know where this should go, or if it is even needed?

C21 Light Green BARO OUT - Barometric Sensor Output is Integra only so I'll have to manually run this to the sensor.

D13 Green/Black SHO2/SG - Secondary Heated O2 Sensor Ground doesn't have a home on my OBD2b computer. Can I ground this to the chassis?

The last wire: I couldn't find an input in OBD2a for the cruise control A5 CRS (on the OBD2b specs). I'm know OBD2a vehicles have cruise control, does anyone know which plug it is?

I'll have to get an OBD2b computer for the California smog *****, but I plan to run it off the OBD2a JDM computer. I'm surprised the DIY I got the specs from didn't mention any of this...



Thanks

 

Here you go

 

I haven't seen those exact pics before, but the diagrams I have show identical info. I got all my info here:
http://www.ff-squad.com/technet/

So I am still in the same boat. Thanks for posting that pic though, it was good to verify my current data.

I'm curious if anyone on here has done a conversion harness DIY style before? The lead that worries me is the Voltage Reference, does anyone know in "reference" to what?

 

i have never seen anyone convert obd2a to obd2b.. you are the first ive always seen obd2 to obd1. but ill help you search and let you know

 

Looks like I also have to re-wire the Dizzy so it will work off my OBD2b wiring harness. The distributor is 9 pin OBD2a big plug dizzy. My OBD2b harness doesn't have the RPM Lead wires (Dark Blue, Black/Yellow) Without these my tachometer wont work. I didn't see these on the ECU pinout, does anyone know which computer terminals these leads run to? I do have the ITR wiring harness so I can clip the female dizzy plug and use it.

One big problem I have is my manual doesn't have a 1999 OBD2a ITR wiring diagram. Mine only have the 2000 ITR which was OBD2b... I am downloading a 98 ITR manual right now. I'll have a look when its done

 

Ok that manual was the exact same as the one I already have... I need OBD2a ITR wiring specs!

 

I'm giving this thread a bump. Does anyone know what to do with the two RPM Lead wires on a OBD2a distributor when using an OBD2b wiring harness? My understanding is these two wires are necessary to operate the tachometer. Problem is I can't find an OBD2a wiring diagram. I have the OBD2a ECU pinout diagram but I need the wiring diagram to see where the two RPM leads run to. They don't run to the ECU I don't think. I think they run strait to the tach. Correct me if I'm wrong.

I'm using the OBD2a P73 ECU. My civic is OBD2b.

Any help would be greatly appreciated. Thanks

 

im incountering this probleme too obd2a harness and p73 ecu but my car is a 00 obd2b im wondering if its worth the hasle to rewire my 2a harness to 2b

 

Aren't there conversion harnesses on ebay for like $50 for this?