sorry for the dumb question but anyone know the wiring for the tachometer like which wire goes to which?... i just bought it and have no clue which wire goes to which

 

i havent installed one in a long time but please correct me if im wrong
black = ground
red= power
yellow = accessorie [sp?] a.k.a which will turn the tach on when the lights/igntion is turned on [depends on how u hook it up]
green = RPM signal

the yellow and green wires varie from color. what color are the wires that u have?