I'm swapping a B16A2 engine into my 2000 hatchback and using an OBD1 ECU with a harness that has OBD2 connectors in the engine bay but OBD1 connectors for the ECU. To ensure everything works correctly, I'm manually checking each wire to ensure it matches up with the correct locations on the ECU and chassis harness. However, I've encountered an issue. The "A" ECU plug is located in the cabin for 99-00's, so I need to depin the relevant connectors and add them to my new harness.

My question is with the K-LINE (A21) and NEP (A19) pins, which don't appear in the OBD1 wiring diagram. I assume the K-LINE is related to the OBD2 diagnostic port and NEP is for the tachometer test connector. Are these two pins necessary, or can I leave them out?

 

Some more information I found, looking at the electrical troubleshooting guide, it looks like on 99-00's, the tachometer is fed from NEP (A19), but on 96-98's its fed from the ICM in the distributor (pin 9). I'm guessing in order to make this work, I'll have to bridge pin A19 from the existing ECU plug to the blue distributor wire (pin 9) in order for the tach to work. Does anyone know?

 

The following is from the 92-95 civic manual, it looks like the data link connector is connected to Pin D7 TXD/RXD. Do I have to connect the existing K-LINE pin to the TXD/RXD pin on the OBD1 ECU?

 

There is no K-line on the OBD1 ecu, so no need to worry about that. The NEP wire, which also doesn't technically exist on the OBD1 ecu is how you will want to get tacho signal to your dash. Best way to do this is to jump the OBD1 ICM pin over onto the NEP wire via the pin in C131 (the green connector) at the ecu.