Wiring mess / advices


New Member
Jul 29, 2023
EG9 , EJ9
Hello guys , I am back after many months with some updates.
I have a civic EJ9 with (not anymore in it) d14a4 , its a prefacelift model 96-98.

I bought a complete swap from an ek4 but I was told its a 99-00 (facelift model)
It came with engine/box , wiring harness , dizzy , axels , rear hubs with brakes , fronts aswell , everything.

Now my car is an SFI (p3y ecu (2 plug ecu).

A friend of mine gave me for free an obd2a to obd2b conversion harness.

Now on Saturday we managed to strip down the car , removed ecu , harness , box + engine and pretty much everything.
Now on Monday , I will go back to the shop to see about the harness , new ecu and such.

If I remember correctly the new ecu has 3 slots , which I am guessing won't work with the dashboard harness of the 96-98.

Is there a conversion harness (dashboard wise to make it obd2b?)
Could I potentially half use the conversion harness that I have (obd2a to obd2b) but only half of it , to basically make it work?
Should I try to source an obd2a b series engine harness and will that work? plug n play or I will have dizzy issues and what not?

My best guess for now , is to basically take the conversion harness plug my dashboard harness into that and then modify said conversion harness to work with with the obd2b engine harness.
its a bit confusing searched 3 forums couldn't find any ideas other than , get a obd2a harness , but even that I am not sure if SFI is basically obd2
Because in dodo-upgrades , I see that SFI is 2 plug ecu and obd2a and obd2b are 3 plug ones.

Super confused , does anyone have any experience with this? would it be simpler to just do obd1 conversion directly?
Engine for now is going to be stock and for the following many years. so no need for tune at least for now.

Not sure , how easy to find an obd1 ecu + engine harness or obd2a engine harness , any input and advice would be highly appreciated!
My last resort is to go pin by pin.
So , after today , I came to the following conclusion:
I have a p2t ecu the obd2b version.

In the first picture is the last connector that remains from the cabin.
The second picture is from the new engine harness (obd2b)

So the SFI has only 2 plugs for the ecu. and the green plug as well.
If I am correct , the green plug is the dashboard plug.

And in the engine harness there is a connection somewhere , that feeds the cluster and lights directly from there.

The same principal I would assume is in obd2b but , there are 3 connectors and only 2 connectors from the engine that fit the ecu and the green one that seems to be fitting to the dashboard one (green one).
Somewhere I read that the third plug is for auto transmission ones but not sure.

Can someone verify that?


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Your solution should be very simple.

I wanted to let you konw some stuff first. ALL OBD1/OBD2A/OBD2B are 3 plug connectors at the ECU. The OBD1/OBD2A engine harnesses will provide all 3 connectors through the firewall at the kick panel for the ECUs. Don't ask me why Honda made it so complicated for OBD2B, but there will only be 2/3 ECU connectors through the firewall while the 3rd one will be acquired from the facelift (99-00) cabin harnesses.

What you need to do now is buy an OBD1 or OBD2A ENGINE HARNESS. This is the best way in my opinion. DO NOT use the OBD2B engine harness you have, that route is an entire headache and mess to get it to function properly unless you want to change out your entire dash along with the cabin harness LOL.
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Alright , then I will try to source that , I was hoping that since it wasnt obd2a and was SFI (which was in europe) would be simpler.
Will obd1 / obd2a be plug and play? or do I need some conversion for dizzy and anything else?

because my thought then after your input is to get the obd2a , and then obd2a -> obd2b ecu adapter and should be set.
What engine do you have exactly? Yes, ideally you would get a OBD2A engine harness and plug into ECU with the OBD2A to OBD2B conversion adapter. All 3 types of ECUs can use the exact same distributor. However, different year distributors will only match with the corresponding engine harness (OBD1/OBD2) because the plug connector is different.
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I have a d14a4 , its a European market engine and maybe in some Asian / African countries.

My ecu that came with that engine is a p3y that has 2 plugs. and the green one.

The swap that I bought is from a 99-00 civic p2t ecu , 3 plugs. but from the engine harness that came with the swap has 2 plugs + the green connector.

its hard to find proper swaps , that's why I bought it from a facelift and 1 of 2 available at the time.

its going to be pretty hard as well to find a 96-98 harness for proper money if any available. that is why I was adamant to make it work. but I need to see what that third plug is all about.
From my research basically I am missing the A plug , which has PCS , SCS , FLR , ACC , MIL , NEP , FAN C, DLC , STS , PSP SW , ACS , ELD , BK SW

PCS – Purge cut-off solenoid
SCS – Service check connector, short to SG2 to read CEL codes
FLR – Fuel relay
ACC – A/C clutch relay
MIL – Motor indication light, provides the blinking light (CEL) signal
NEP – Signal to engine speedometer driven by ECU
FANC – Radiator fan relay, not always present
DLC – Data link connector
STS – Starter switch
PSP – Power steering switch, not always present
ACS – A/C switch
ELD – Electric load detection, not always present
BKSW – Brake switch, not always present

Might be more than that..

Which means that the car won't even start. but I might be able to repin it via the adapter harness. have to check it out tomorrow or in the next days.

For reference , this is my current pinout : https://dodo-upgrades.nl/index.php/pinout-sfi/
Well , did I little bit more thinking and realized, that this will not work because on SFI like EJ9 , its like obd2a where everything comes from the engine harness so basically , not even sure how to create the A plug , which back to square one , source an obd2a engine harness and maybe convert the dizzy plug from obd2b to obd2a
Well , did I little bit more thinking and realized, that this will not work because on SFI like EJ9 , its like obd2a where everything comes from the engine harness so basically , not even sure how to create the A plug , which back to square one , source an obd2a engine harness and maybe convert the dizzy plug from obd2b to obd2a
as this and above.

Source the correct harness and then change the plugs you need to, its quite a simple process to change them