what is this plug

[4G63CORDIA]

I have a plug that I cant figure out what it goes to. I have a 4G63 i am putting in a 1986 mitsu cordia. I think it connects to the chassis harness. It is located inside the car by the ecu on the engine harness. Also i was wondering about the 91-94 in a 90. I have a 91-4 harness/ecu and a 90 motor. I read the faq about the conversion, but i am a little confused. Do i need the noise filter? Also the motor didnt have an ign module. I bought one from a friend. If it is a 91-4 module, do i still need to do the wiring change?

Here are pics of the plug in question. If you know, i need to know what each wires goes to.

4 wire plug.

black/yellow
black/white
black/red
yellow/green

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