tach wiring ???

[78 Sprint]

I bought a new autometer tach it says it should be hooked up as follows one goes to ground, one is the signal, and one is 12v ignition switch, does the 12v ignition switch wire hook up to the battery side of the ignition swith or the ignition side of the switch. One more question my old tach had just a signal and a ground post no 12v ignition hooked up to it what is the difference. do i need to hook up the 12v ignition wire on the new tach.

[Sleek-Jet]

Yes, hook it up to the ignition (switched) side 12V source ie, a 12V source that is hot when the key is "on", and cold when the key is "off".
Otherwise the tach will run the battery down.
The signal and ground wires should hook up to the same spots as your old tach.

[78 Sprint]

Thanks for the information guess i should put the battery in it and check the swicth with a test light to be sure all it says on the switch is battery, ground, and ignition.

[Sleek-Jet]

Do you have any other gauges??? If so, you can tap on to the 12v they are using. They should be on a switched 12v. :idea: