67 Hood Tach install
 

I posted this is the Electrical section but I figured I would try here too in case anybody has had this issue on their 67...

Hi,
I did a search and cant find the answer im looking for. Maybe I missed it or maybe my situation is unique.
I had an older repro hood tach on my 67 GTO. I was cleaning it and broke the needle so I purchased a new hood tach from our sponsor.

I plugged the new tach into the existing plug where the old tach was plugged in and the new tach lights up real nice and when I turn on the car the needle goes all the way to the right then back to zero and then wont move. I was assuming the new tach would use the same wiring as the old one?

I have an MSD6AL #6420 and a MSD tach adapter PN 8920. I did not change anything, I just simply plugged the new tach into the old plug that was working fine.

Any suggestions? I'm very electrical challenged and that's why I was hoping I could just plug the new one into the old plug.
Thank you!

See my comment in Elec.