OBDI.5 to OBDII Engine bay harness fixes

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3X00-Modified
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OBDI.5 to OBDII Engine bay harness fixes

Post by 3X00-Modified »

Well here is a short write up on how to modify the 96 OBDII harness to work in a 94 or 95 car, without changing the interior harness. This gives you the ability to tune a 94-95 car with DHP or HPTuners. Info needed on tuning PM me.

Some may not feel comfortable doing this but others can accomplish it easily.

There are three fixes you need to do to make the harness work on a 94 or 95 interior dash harness.

Re-route Tach signal wire from pin 9 on the ECM connector to pin C on the ICM connector. (IF YOU HAVE A TACH DASH) This is not necessary if you do not have or ever want a tach cluster.

Re-route Pin G5 on the driver's side body harness connector to Pin P on the passenger side body harness connector.

Tap pin F4 on the drives side body harness and connect that to the engine harness side of the wire that was on Pin P on the passenger side body harness, wire is left over from the previous step.

Then you can add some wires that tap off of the passenger side body harness connector to wire in your com port, I'll add pics of that part later.

The steps: (all relating pictures below the step being described)
Find Pin 9 on the clear ECM connector, WHITE WIRE.
obdii writeup 001.jpg
Cut it 2 inches back from the connector just to leave some extra if you ever want to hook up a 0-5v tach setup.

Pull the wire back through the passenger side firewall connector.
obdii writeup 002.jpg
Pull it back to where the wires for the ICM come out of the main harness.
obdii writeup 003.jpg
Route it up to the ICM connector to determine length of wire needed.
obdii writeup 004.jpg
Pull a connector from a un-used connector you have lying around, remember it has to be the same type of pin, TPS, Crank position, IAC, and a few others are all the same, I cut up a old crank position connector to get the pin out of it.
obdii writeup 005.jpg
I cleaned it up trimmed back the wires, threaded the white wire through the ICM connector first at PIN C, and then put the pin on the wire and soldered it together.
obdii writeup 006.jpg
I then pulled the wire back into place clipping the pin into the connector.
obdii writeup 007.jpg
Cut the white wire on the driver's side body harness connector, PIN G5 AKA top row second from left, Looking at the back side of connector, as pictured, (natural wire curve aiming down)
obdii writeup 010.jpg
Pull this wire back through the harness to the ABS ECM plug.
obdii writeup 011.jpg
Stage this wire there for now.


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Re: OBDI.5 to OBDII Engine bay harness fixes

Post by 3X00-Modified »

Cut the pink wire PIN F4 on the driver's side body harness to allow you to tap in a new wire to run to the other side.
obdii writeup 012.jpg
Solder the new wire to the existing wire and then connect all three ends back together, cover with heat shrink and wrap in electrical tape.
obdii writeup 013.jpg
Now run this new wire through the main harness taping the harness back up as you go, once you get to where the ABS plug is, start to pull both the new wire and the white on you cut from the previous step, route these two wires over to the passenger side compartment entrance. Connect them to some tool you can use to thread the wires through the grommet, I used welding wire, a coat hanger is fine as well.
obdii writeup 014.jpg
Pull the two wires through the passenger side grommet.
obdii writeup 015.jpg
Route them over to the rectangle body harness connector with the blue and red clips on it.

Now cut the wire at PIN P giving you enough wire to work with on either side.
obdii writeup 016.jpg
Now solder the corresponding wires to the ends pictured here. White wire is the ABS plug wire, this goes to the connector side, and the yellow wire is the new one that I ran from the driver's side, this one goes to the harness side, going back out to the engine bay.
obdii writeup 017.jpg
Com port wires are as follows, going from the com port to the rectangle body harness pictured just above this.

Orange - to any 12V constant source
Black - Any Ground
B/W - Tap to Pin D on the rectangle body harness (Engine bay side of this plug)
Purple - Tap to Pin E on the rectangle body harness
Tan - Tap to Pin F on the rectangle body harness

That should allow you to connect to the ECM and flash and get codes. Mine is wired right to the rectangle body harness plug and is positioned on the passenger side to prevent annoying DHP cable cross over.

That's all I have for right now, any questions feel free to PM me, or reply to this post.


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Re: OBDI.5 to OBDII Engine bay harness fixes

Post by Themanytoys »

Photos are not loading up. 😢


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Re: OBDI.5 to OBDII Engine bay harness fixes

Post by 3X00-Modified »

Themanytoys wrote: Wed Apr 05, 2023 5:12 pm Photos are not loading up. 😢
Fixed, but this is really kind of obsolete since OBDI.5 is tunable.


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Re: OBDI.5 to OBDII Engine bay harness fixes

Post by woody90gtz »

Jay has been tuning OBD1.5, but I know he was still interested in this swap.


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Re: OBDI.5 to OBDII Engine bay harness fixes

Post by Rettax3 »

3X00-Modified wrote: Mon Apr 10, 2023 10:10 am
Themanytoys wrote: Wed Apr 05, 2023 5:12 pm Photos are not loading up. 😢
Fixed, but this is really kind of obsolete since OBDI.5 is tunable.
Thank you Jon. I would say that at this point, NO information is obsolete (in a relative sense). Not everyone will have the right tools to tune OBD 1.5, but might be equipped for OBD II. And there are other reasons to 'upgrade' to the OBD II also, perhaps due to available replacement parts -those OBD 1.5 PCMs are not going to be easy to find now days... Your time putting this in order is appreciated.


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