idiot question about obd1 and obd 2a
 

here is my dumb ass question if i have an obd2a car and i have an obd1 engine and engine harness will they plug in and work i know that i need the obd2a to obd1 ecu harness i just want to know if i can use my obd1 engine harness or will i need to get an obd2a engine harness. thanks