So I delivered a new wiring harness to my mechanic for my 1988 300Zx he says it wont fit! The parts guy swears he has sold a dozen or more with none coming back! Is there a trick, or what? How do you get these wired in?

they may come back, their still working on installing them .I would assume!

The part supplier only list them as being Fuel injector Plug harness 84- 89 (6) NOS I don't know engines at all! I bought this car 4 years ago when my daughter turned 16, she didn't want it so I started driving her and fell in love! However I haven't been able to pin point the nature of her driving so ruff. I recently had her inspected and all they could find was corrosion on the wiring harness! Any help appreciated!

dont waste your time on a harness if its not really too shabby.look to normal reasons for running bad,then see if needed,start with plugs,fuel cleaner,correct line pressure ,and air flow ,and clean mass flow sensor with a non harsh chemical like window cleaner,timing if can do also it all adds up,assuming this car was never molested by a tinker do it myself owner without any knowledge ,just rip and tear

1988 z uses an offset nipple. The earlier 300zxs used an injector plug that has a nipple centered. That is most likely the issue you are running into.