I know this is an old post.... But I just ran it to this little confusion with the Autometer 9117 tach adapter.... You need cut into pin #34 (SOLID RED Wire) in the harness under hood passenger side on the firewall.... The big square one with the 10mm Bolt in the center. Like someone said above, Cut the wire BEFORE the Coils. I wanted to post which exact PIN # it was so if someone searches for it they can have an answer.