I am trying to figure out why my tach does not work. From searching I have seen that the green wire from my - term on the coil goes to the tachometer. The tach also has a black (ground) and red/black (12v) wire on the back of it (along with light bulb wires).

I have tested for breakage in the green and black wires and they read fine with the ohm meter. Power reads 12v from the red/black wire and ground.

When the key is on, 12v, when the car is started and idling it drops down to about 6v-7v. When car is fast idled the voltage increases again up to 12v.

With this information, am I believe that my tach is toast? Is there anything else I can test that will give me my answer?

Thanks in advance for the help!
Jim

74 260z, bone stock, su carbs.....reentered zland finally!

 

i discovered that under certain circumstances (which unfortunately i can no longer remember) my tach went out because my alternator was bad, or there was a serious short somewhere in my system. my car's got electrical gremlins that i have been too busy and poor to really chase down, and its something that has come up once or twice. i must have nailed that particular gremlin tho, because its been a while since it bit me (or else i could remember more detail)

 

I obtained an external engine analyzer with tachometer in it, to sync the carbs. I went and hooked this up to the wires that plug into the tach and it got reading just fine.
This must mean my tach is bad correct? These things are so damn expensive (from MSA). Guess I'll have to go junkyard hunting, unless someone has one for a decent price.

 

junkyard first, its easy and no shipping, probly cheaper.

otherwise, just hold out, search this site, zcar.com, and other similar places. they do come up. if all else fails, ebay.

 

majority of 73/74 Z tachs go bad - it's a burnt out resistor in the tach itself. I'd just replace it with a nice 5" tach from autometer - it fits right into the stock pod