vtecb8

Hi

I'm doing a engine swap. D16Y to B18c obd1---Car is 1996 Honda civic EK, NZ New, sohc vtec, manual

I have both looms.. obd2a in my car right now and obd1 integra loom

I've been told i can just change plugs around

Here is the confusing part

1) current civic loom alternator has 3 wire plug
2) B18c loom has 4 wire plug

What wires do i connect? and what do i do for the extra 4th wire?
If i dont have to connect the fourth wire do i have to unpin it from the ECU (obd1)? im running a jumper harness from obd2a to obd1

Thanks