OBD2a to OBD1 Harness Pinouts

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CW FL5 CTR
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Joined: Wed Apr 17, 2024 10:17 pm

OBD2a to OBD1 Harness Pinouts

Post by CW FL5 CTR » Mon Apr 07, 2025 6:46 am

I'm in the process of converting my chipped P28 w/ V-AFC setup to a P28 w/ Hondata S300. I wanted to keep the OBD2a to OBD1 harness intact with the V-AFC soldered in, so I ordered another OBD2a to OBD1 harness so I could swap it out. I connected the new harness with the same P28 and the engine cranks but does not start. I plugged in the old harness and it starts right up. I compared the old harness with the new one and noticed the new one has fewer wires than the old. I also noticed that some of the wires in the car's harness aren't connected in the new harness (since it has fewer wires in the new harness). I thought this was an incomplete harness but noticed others for sale had the same missing wires as the new one I have.

Not sure what is going on, is it normal to have wires from the car's harness that are not connected? Maybe I have something hackish going on with my old harness, I have to undo the electrical tape and see if there is something custom wire connections, but I can't imagine anything other than the V-AFC wiring spliced in.
'23 CW FL5 CTR
'98 CW DC2 ITR

Dave7CDMTYPER
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Re: OBD2a to OBD1 Harness Pinouts

Post by Dave7CDMTYPER » Mon Apr 07, 2025 9:22 am

I don't know but curious to see some photos.
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2001 GS-R
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AzhotR
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Location: Arizona

Re: OBD2a to OBD1 Harness Pinouts

Post by AzhotR » Fri Apr 11, 2025 4:52 pm

Do you know if your ECU is getting power when your cranking it? What conversion harness are you using? Do you have a laptop with SManager installed? If so open smanager and connect the ecu to computer via usb. When you turn the key to the on position SManager should recognize the s300.

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