i have a 79 trans am and im tryin to get my tach working, it has a seprate plug with a power wire and tach wire that plugs to the back of the tach, the power wire shows 12 volts but my test light shows nothing on the tach wire with the engine running, not sure if i can check it with a light or not and thats what i need help on, let me know how to check the wire, thanks allen

 

I think the tach wire signals to ground as the engine fires so it's not going to show a voltage, although if you put your meter to 12v source and ground to the tach wire you should see a reading on your meter.

 

The tach wire will be too high a voltage to read with a light or meter. It should connected to the -neg. side of the coil.