Most obdo cars are peak and hold injectors which needs a resistor box and most obd1 ( not h series) are saturated not needing a resistor box. When looking at the obd1 injuectors where they attach to the plug, they have a plastic piece in each top corner. When looking at the obd0 plugs they have the plastic piece in the middle top only. I know this sounds confusing but when you look at them in person youll see what I'm talking about. If you need any thing else let me know.