Anyone needing to map wires or convert harness from one OBD to another I just put together a nice diagram to help. All the way from OBD2 down to OBD0 since I am doing this for my VTEC project, hope it helps someone else too.

 

Do you have the OBD2a spec to add to it?

 

Good call, I'll see if I can dig it up and re-do the diagram with OBD2A/B

 

I've updated the diagram, if anyone could please verify and double check my work it would be great.

Got updated info, if anyone is doing this; there is a BLUE wire coming from the OBD0/OBD1 engine harness this is for the Tachometer output which OBD2B does not have (OBD2A does).

Simply run a wire into the distributor housing, and tap into the ignitor housing there is a lead that is not used it is at the base of the rotor assembly impossible to miss; this should send the proper signal.

Reason is that OBD2B ECU gets RPM from the other sensors (CKP/CYP). But in my case running with a P28 OBD1 ECU needs this readout.

Now to see once put all together if it works...

 

Nice catch on the RPM signal for the OBD2B distributor. I was just about to point that out.

 

With all the distributor pinouts on the internet im going to take a chance and go with this one. Before I start cutting and soldering, can somone confirm this one is good ?? Everyone and their brother likes to make one of these, some with varying wire colors and positions. wish we could erase the internet of all of these images and have one agreed upon diagram.

 

I dont follow the underlined comment, ive heard that the blue rpm wire from OBD1 can run into the dash cluster ??

 

yes the wiring is correct
in my build thread
(Marcos new work car 90 sedan)
i am running the obd2 dizzy
wired just like in the picture with no problems for over a year now