hood Tach
 

ISO wire pinout on the 3-cavity connector for hood Tach. The wire colors are too far gone. I have found two (of the three wires) of the wires are going to the back Light. and assume the third wire goes to the coil. What I don't know is the polarity of the GND & 12v wires. (which cavity is ground, which cavity is Ignition power). I know the incandescent bulb doesn't care, but I'm assuming the Tach module will. I don't want to hook up backwards and fry the Tach with the wrong polarity.

Any help would be appreciated. Thanks