Probably a really dumb question, I'm just overthinking and confusing myself. I have a 1993 Honda Civic SI (OBD1) and a b18LS (OBD2) motor. Here's my questions. First off engine harness, mine looks like a jungle right now so I'm just going to get a new one but what harness do I get? Do i just get a regular b18 LS (OBD2) engine harness? And ECU, right now i'm on the P28, but going to get s300. Do i need to get a OBD1 to OBD2 jumper harness for the ECU? Just really confused myself with all of it and trying to look for what i actually need so i can get going with my car.

 

What is wrong with your harnesses is it all cut up or does it just need to be organized? You should try at all costs to avoid changing that harnesses because its the whole dash harnesses in obd1 vehicles. Obd2 vehicles have an engine sub harness that is separate. If your going to use s300 obd1 is really a must, and there is no sense in wiring your car up for obd2 just to use a jumper harness back to obd1.

 

If the OBD-2 LS engine comes with a USDM engine harness, it will plug in directly to your '93 Civic chassis harness at both shock towers. Since you intend to use a Honda s300 for tuning, I suggest you socket your existing P28 and place the s300 in it. You can upload a B18B map which deactivates your VTEC circuit pathways in the ECU, but if you add a VTEC head later, you will be able to alter the calibration and fully support the functions of the VTEC head. If you don't intend to use the s300 right away, you could substitute a '94-95 LS ECU (37820-P75-A01) and it plugs directly into your car.

 

The good thing about 92-95 civic is you can use a harness from 92-95 civic or 94-01 integra. Now to figure out which harness to use depends on what distributor,injectors and alt your using. The distributor,injectors and alt tell you which harness you go with as 92-95 is obd1 and 96-01 is obd2.