When I turn the key to start, the needle on the tach goes to 8000. I just removed the tach to change out the lights and when I checked the contacts, nothing went to ground except the black wire. When I checked the dash wiring, I got 12 volts on the green wire. On the tach, I got 4000 ohms from the single post terminal to it's housing and 320 ohms between the posts of the dual terminals.

Is my problem in the wiring harness or the tach??

I spoke with nhspeedometer today and they told me I could not test my unit without some special meters. They will test the tach for no cost other that the return freight. If they need to rebuild it, the cost is about $ 185.00 plus freight.

installed the rebuilt unit today and it works great. Nice to see the car idle at 600 RPR rather than 8000 RPM

Ed,

Who is nhspeedometer? Where are they located? Do they have a website?