70 GTO Tach
 

I just installed a new in-dash tach to replace an in-dash clock. I was having problems starting the car and removed the ground from the tach and was able to start the car. If I touched the ground to good ground the car would die if I didn't hold the car to about 1500 RPMs. I think the connection for the tach lights might be connected to the ACC power, will that cause this problem? If not what else can I check?