Generally, you want to keep the same year with the same year AND same model with the same model.
If your car is pre89 you'll be wanting the pre89 harness (and some of the pre89 electronics ----- this is the YELLOW plug series), pre89 ECU and pre89 motor mounts. And if the car is 89+ then you'll want the 89+ parts.
EDIT: If the plug colors are the same but the connectors are different then it isn't for the same model.
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