Tick Tock Tach quit working but Clock works

[bad88ttop]

So, over the winter I decided to overhaul the drivetrain on my 70 Charger. When I reassembled it the factory tick tock tach quit working. The clock works but no good for the tach. I checked the connection on the (-) side of the coil and also at the plug on the firewall; no connection issues. I assume since the clock works the tach has power and I also confirmed all fuses are good.
Does anyone have any ideas what I can look at? I find it unlikely the tach went bad all of a sudden, I'm thinking it's something technical. Any feedback would be great. Thx

 

[davek]

you do have both wires hooked up on the back correct?

 

[RJRENTON]

One wire is the 12 volt source to power the tach, the other wire (possibly gray in color) is the wire coming from the coil that provides the RPM pulse that the tach interprets. If you accidently reversed the connections, nothing works. The clock is powered from the pigtail connector separately from the 12v powering the tach.
BOB RENTON