Tach likes to read less than 0

Just got through making new wiring harness for engine and forward harness. Took my time. followed wiring diagram and surprise, surprise, everything works. Everything except the tachometer. When I turn ignition run position or start the engine, the tach shows reading less than zero. Removed the Green wire that goes from negative side of coil to tach when I was redoing harness and reattached to negative side of coil when connecting harness wires to temp sending unit, oil pressure sending unit, ballast resistor, and alternator.
Green wire from tach to negative side of coil is getting current when ignition switch is in run position. Red wire from tach going to ignition switch getting current. White wire from tach connected to dash lighting getting current. Black wire grounded. Have checked all connections and all is tight.
Beginning to think that I did something that may have caused diode or something else inside tach to burn out.
Any ideas as what I should try or do? Should I just get a new tach? Tach I have now is an Autometer.