New tach problems

[ChevyC102007]

I bought a Sunpro SuperTach II from Summit and it got here Thursday (ordered it on Saturday) Anyways figuring that since I had this weekend off work Id go out and install it on the truck.

After alot of cussing (wasnt the tach it wa a couple of my ignition connection came apart) I got the dang thing in about 45 minutes ago. I fired up the truck expecting to see the needle hovering at around 600 rpms at idle......................nothing, lose ground. Shut the truck off and grounded it to another spot. Started it back up....it works............wait a second...........the needle went BACKWARDS as my RPM's increased. WTF!?!?!

I sent Summit an email asking what the problem could be but it might be Monday or Tuesday before I hear anything back Im hoping someone on here has had the same problem or has an idea what it could be.

Before I forget the truck has a HEI ignition on it that was installed by the previous owner (with my luck the dumb things about to go bye bye on me).

Thanks......this just puts the cherry on a screwed up day