69 Barracuda tach

You all were so helpful on my last electrical issue and got it resolved I'm down to the last problem when I turn on the ignition switch the tach goes to max and doesn't return or move till the switch is turned off. It and the distributor are wired to the - side of the coil and even if i unplug the grey wire it stays maxed out. When I unplug the blue wire from the fuse box it goes down also. Thanks in advance for any help.