Faria tach(7000 rpm for outboard) won't work with my Suzuki DT115

[contractor]

Thanks to all of you that have left messages for me with things to try to get this tach to work.<br />I've done each thing suggested, but nothing seems to work. I've used Faria's tech page for troubleshooting. I have 12 volts at ign. terminal. I've used a jumper from grnd post to signal post to check tach. Should show full tach.<br />It doesn't move. Tech sheet says bad gauge. Got a second brand new one. Exact same results.I've checked the yellow tach wire from the gauge to the motor and it reads good. This boat did not come from the factory with a tach. So I'm adding it along with other gauges. All others work fine. The Faria direction sheet says the ground for the tach can come from any point. I've got mine on the ground bar inside the console. I wonder, would it make a difference if I was connected to the ground wire in the harness from the engine. Any thoughts??????