As stated in the title this is my current situation.

2000 Civic Auto
B18B1 Manual Swap(bought the car this way; already a bad idea)

I spent weeks modifying the OBD2 Harness that was on the car(IACV, CFK, extending IAT etc) and running but I could not rid the last few codes of: o2 sensor and IACV after running through countless threads. What took me over the top was the o2 harnesses were sliced and I could not find them to save my life after extending from multiple locations thinking I had the right 4 wires. THERE IS NOT ONE PICTURE ON THE INTERNET SHOWING A PICTURE OF A 99-00 CIVIC CONNECTED TO THE o2 PLUG! >.< to get a visual and the color codes weren't adding up in the diagrams.

Back brief; what's sitting in the garage parts bin:
-94 LS Integra AUTO(frame rail damage I haven't had the patience to get correctly fixed) ie. Parts Car that I stole tons of plugs for in trying to revamp the OBD2B harness)
-OBD1 P75-A51 Auto ECU(removed auto resistors)
​​​​​​-Wireworx Mil-Spec Quick Disconnect at firewall OBD1 Harness

Before I get the, why didn't you grab a EX 5-Speed Harness and a Jumper Harness, keep in mind I was still at $0 spent cause I had this stuff laying around. Called up wireworx and they told me "that's a custom harness, we can make you an interface to run across to the tower harness." Paid. Shipped. Car's not running, fuel pump not priming, no spark and all ground were swapped upgraded, fuses good, auto harness modified to start the car like normal.

From what I'm reading, the under-dash engine harness on the 99-00 OBD2B AUTO vehicles is where the fuel pump/relay are located but I cannot find the pinout for the underdash engine harness.

Currently:
Car won't start(no fuel or spark either I believe)
Brake light comes and stays on soon as I connect battery power
No type of ABS, SRS, Check engine light flash sequence when I turn over the key position #2

It looks like I'm going to have to de-pin the fuel pump/relay from the harness going into the ECU and bring it over the custom sub harness but I can't confirm. ULTIMATELY I'm going to be pissed if they had me buy a sub-harness when I could've just grabbed a harness I know would've worked and sold off the custom OBD1 I had built some time ago.

Pix of the interface, backside of the chassis underdash engine harness, and me pulling the shock tower harness back into the interior and connecting it to the interface plug. All electronics work in the car but she's not starting up. Once again I have a 94 Integra parts car sitting here I can take any and everything from if necessary.

 

99-00 civic are obd2b except hx model.

 

Correct, that was a typo...hence why I'm trying to find the pinout for the harness the OBD2A fellas don't have to worry about

 

If you're going to repin an obd1 harness to an obd2b theoretically you just need to worry about the ecu plugs. Since an obd1 civic/integra harness is designed differently you'll need the passenger shock tower harness and convert the driver side shock tower obd1 plugs to obd2b plugs

edit: I fucked up. You just need to focus on the ecu plugs and nothing else. ffsquad has ecu pinouts for both obd1 and obd2b.

regarding your o2 wiring and iacv error if you can post the cel it would be helpful but I'm thinking you need to do the 3 wire to 2 wire iacv. For the o2 I have no idea what was cut but most wires didn't go 'directly' to the ecu, probably just 1.

 

That's a start, I appreciate it...it's electrical for sure because the car was running perfectly fine before swapping out the harness so it's something small I'm just not getting it. I do wonder why only a select few pins were used with the custom interface adapter harness when it came to the shock tower plug and the under-dash harness. Hoping to get a response this week. I'm going to dive into the pinouts of the ECUs for now.

So the codes were: 70(Automatic Transmission), 10(IAT), 14(IACV/EACV), 41(Prim O2), 54(CFK), 65(Secondary O2). I ridded all of them but the IACV and O2. Ironically the 2-wire conversion for the IACV was already done so just for the sake of it I went to do the ECU harness for the repinning of the harness and still had the code. I do believe there may have been a break in the circuit somewhere else possibly.

Now I'm committed to making this work, from the looks of it...I'm going to be the first person ever to get an OBD1 harness functioning in a OBD2 vehicle cause info on this is non-existent; the irony in the Honda world. We got k-swaps in EFs but I can't get this thing to work...

 

Think about how aconversion harness is made (obd2b to obd1), they are just moving the pin into their respective locations. Thats it.

 

I'm just realizing the ECU isn't getting power, all cluster lights illuminate full and bright but the check engine light is extremely dim. Going to try to trace some wires; the factory harness had 3 grounds leaving the terminal, my tucked harness only has one wire.

 

Oh boy... More issues

 

Updating for future thread searches. Getting closer.

Took a test light to the main relay and noticed the relay starts buzzing when I hit the yellow/black wire which is an indication of a bad ground. Thermostat ground is solid.