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Discussion Starter · #1 ·
A few days ago I made a post about some wires which didn't match up between my OBD1 engine harness and my OBD2A main vehicle harness. After some more research, I've learned that the 3 wires pictured below are responsible for the Crankshaft Fluctuation Sensor (blue/red and white/red) and the EVAP Purge Solonoid (red) respectively. These 3 wires are from the OBD2A main vehicle harness.

While these 2 wires from the OBD1 engine harness are both connected only to the EVAP Purge Solonoid:

The reason for this discrepancy is that the OBD1 engine never came equipped with a CKF sensor, whilst the later model OBD2 vehicles did. I'm running a P72 OBD1 ECU through a conversion harness for this car, so I don't believe my car's computer has the ability to even read a CKF sensor error. That being said, I have found this page (archived for future generations) which details a way of bypassing the CKF sensor entirely so it won't read a check engine error on an OBD2 build.

Mainly, my big question is this: How is this EVAP Purge solenoid actually meant to be wired? The OBD2 main harness only has the one red wire coming off of it, while the EVAP solenoid requires a red and a yellow. I also found this forum post, in which user JimBlake says one wire runs to ECU pin A20, while the other gets power from the main relay. He says "The ECU closes the ground side of the circuit when it wants to energize the relay". Unfortunately, he doesn't indicate which wire goes where, and testing continuity on both my OBD2 and OBD1 main harnesses I've been unable to find an electrical path between A20 and either of the red or yellow wires.

Any help on this would be seriously appreciated, I've called around to the "honda specialists" in my area and none of them have much of a clue about engine swaps or wiring. Thanks
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