Skip white Hei distributor tach wiring help

[arh]

I have been running a skip white hei distributor for a year now with no issues in my 69 barracuda. I purchased an in dash tach from year one and decided to test it before pulling the cluster out. Hooking it up the way it says 12v source and neg side of coil output I get no reading on the tach. HELP

 

[70aarcuda]

got a good ground?

 

[arh]

There are only the 2 wires. Both seem to be connected well

 

[70aarcuda]

every tach i have owned needed to be grounded to compete the circuit..

 

[arh]

Thank you for your help. The tach has a plastic housing and one of the mounting points has a wire to it. Grounded and it works perfectly

 

[70aarcuda]

Good..........