Gauge issues after Tach install

[camoit]

The first question that comes to mind is did you flip the switch in the back to 4 cyl?
I forgot to set mine to 6 when I started up my truck for the first time. All tachs come set to 8 cyl from the factory.
Next what model do you have?
The green wire should go the - on the coil. The red needs to go to 12 Volt. Do not hook it to the + side of the coil. That is not going to be a full 12 volt. Black to ground of course and leave the white off for now. You can worry about illumination later.
Also check the ground from the engine to the firewall.