You should NOT tap into a wire directly from the ignition coil itself to connect your tachometer. The high voltage in that system is extremely dangerous and can damage your tachometer or even cause injury.
The correct way to connect a tachometer is to tap into a wire with a low-voltage signal that reflects the engine's RPM. This is usually found somewhere in the engine compartment or inside the car's fuse box. Looking for a wire that goes to the computer (Engine Control Module or ECM) is better, as the ECM has a processed, clean signal.
Here's what you should do:
1. Consult your car's wiring diagram: A wiring diagram specific to your 1992 Cavalier's engine (1.8L or 2.0L) is crucial. You can find these diagrams online (often on sites like Haynes or Chilton repair manuals) or at a parts store. The diagram will show you the correct wire to tap into for the tachometer signal. It'll be labeled something like "Tachometer Output," "RPM Signal," or similar.
2. Locate the ECM: The ECM is usually under the dash or in the engine compartment. The wire you need will likely originate here.
3. Use an appropriate wire tap: Don't cut into the existing wires. Use a wire tap connector to safely connect your tachometer wire to the correct wire in the vehicle's wiring harness.
4. Use a multimeter: Before connecting anything, use a multimeter to verify the wire you found is indeed providing the correct RPM signal. The signal will be a pulsing DC voltage.
In short: Don't try to find a wire at the ignition coil. Find the correct low-voltage signal wire according to your car's wiring diagram. This will be safer and more reliable. If you're not comfortable working with car wiring, it's best to have a qualified mechanic install your tachometer.
