Easy way to upgrade OBD I to OBD II
That is interesting. Thanks for the link.
What would be wrong with fabbing up a custom subharness to covert the plug for an OBD I to an OBD II system, then adding extra wires as necessary?
I'd bet all they do with the conversion harness is cut the plug off and crimp new ends on the wires for the new plugs. Might even be that the pins are the same and you could de-pin the OBD1 plug and stick them in the OBD2 plugs. Oh, and add missing wires for things like the transmission controls.
So, I would say that yes, you could build a custom sub-harness to convert it. I see similar setups for all kinds of other makes, and I think there used to be one for Mopars. Trick will be finding a male plug that fits the OBD1 female plug.
Only hang up I can see is injectors. Wiring should be the same at the ECM, but Mopar changes the injectors several times over the years, and they don't all take the same connector. Wouldn't be an issue, except that the flow rates changed over the years, so you will want to match injectors to the ECM which could require conversion harnesses to plug the injectors in. I have seen those as well, so I am sure you can buy them.
One other issue to be aware of is the method of control for the cruise control module. It's not the module and plugging it into the ECM that is the issue, it's that the ECM has a different method of being signaled. In the OBD1 setup, the cruise switches worked different pins on the ECM to tell it on/off, set/resume, etc. The OBD2 ECM uses just one or two pins and variable voltage through the switches to tell the computer what to do. I think the way the conversion harness solved this was to add resistors into the wires in the harness and then gang the outputs to the pins as required.
