1. Gather Your Tools:
* Multimeter: This is essential. You need one that can measure DC current (amps). Auto parts stores sell inexpensive ones suitable for this task.
* Test leads: These connect the multimeter to the car's electrical system.
* Penlight or flashlight: For working in dark areas under the dash.
* Patience: This process can take time.
2. Basic Checks (Before Advanced Diagnosis):
* Interior Lights: Make absolutely sure all interior lights, glove box lights, and trunk lights are OFF. A simple stuck switch can cause this.
* Radio: Check that the radio is completely off. Some radios draw a small amount of power even when turned off.
* Aftermarket Accessories: Anything added to the car after it left the factory (alarms, remote starters, aftermarket stereos, etc.) are prime suspects. Disconnect these one by one to see if it resolves the problem.
3. Measuring the Parasitic Drain:
* Disconnect the Negative (-) Battery Cable: This is crucial for safety. You'll be working with the car's electrical system, and disconnecting the negative terminal prevents accidental shorts.
* Connect the Multimeter: Set your multimeter to measure DC current (amps). The range will depend on your meter, but start with a low range (e.g., 10 amps). Connect the red lead of the multimeter to the positive (+) battery terminal. Connect the black lead of the multimeter to the disconnected negative (-) battery terminal. The multimeter should now display a current reading.
* The Reading: A perfectly healthy car should show a drain of around 20-50 milliamps (mA) or less. Anything significantly higher indicates a problem. Note the reading.
4. Isolating the Drain:
This is where it gets more involved. You'll need to systematically disconnect fuses and circuits to pinpoint the source.
* Fuse Panel: Start with the fuse panels (usually under the dash and in the engine bay). Begin by disconnecting fuses one by one, observing the amp reading on your multimeter after each disconnection. If the reading drops significantly after removing a fuse, the problem lies in the circuit protected by that fuse.
* Repeat: Continue disconnecting fuses until the drain decreases to an acceptable level (20-50 mA). The last fuse you removed protects the circuit with the parasitic drain.
* Component Identification: Once you've identified the problematic fuse, consult your owner's manual to find out which components it protects. This will narrow down the possibilities to a specific system (e.g., power windows, radio, interior lights, etc.).
* Further Investigation: With the problematic circuit identified, you may need to test individual components within that circuit. This may require more specialized tools or the expertise of an auto electrician.
Important Considerations:
* Safety First: Always disconnect the negative battery cable before working on the electrical system.
* Patience: This is a methodical process. Take your time and carefully document your findings.
* Professional Help: If you're uncomfortable working with car electrical systems, don't hesitate to take your car to a qualified mechanic or auto electrician. They have the tools and expertise to diagnose and repair the problem efficiently.
By following these steps, you should be able to pinpoint the source of the parasitic drain and get your Bonneville back on the road. Remember safety first!
