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| Joined: | 03-12-2005 |
| Location: | Kingman, Arizona USA |
| Posts: | 532 |
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Yes, you can test a tach that way.
The green wire is the power supply for the tach. This should be +12 volts when the ignition switch is ON. The black wire connects to the body of the tach, and goes to chassis ground.
My wiring diagram claims that the two remaining wires are both white but in many cars one of them is white-grey (AKA white-slate). In any event, one of these wires comes from the ignition switch and should read +12 volts when the switch is ON. The other wire goes to the ballast resistor in the engine bay. The far side of the ballast resistor goes to the + side of the coil, and to the terminal on the starter solenoid that bypasses the ballast during cranking (only).
I don't know whether the male pin on the tach goes to the +12 volts or to the ballast, you'd have to check your wiring harness.