Technical Dixon Tach help

We have a small Dixon blue line tach and 3 other Dixon blue line gauges in my wife's 64 Chrysler. The back of the tach has 3 posts, S, - and +. When hooked up to positive battery, negative battery and S to the coil the tach goes to full RPM. Any help is greatly appreciated. Yes I did searches!

 

Why have you got two wires on the + and nothing on -?

 

We ran a wire direct from battery trying to prove it. Photo was taken when replacing the ground.

 

Here is a Hamb post on Dixco tach wiring from 2012 that might help..

Dixco Tach Wiring. | The H.A.M.B. (jalopyjournal.com)