The article provided some helpful troubleshooting hints. There are two schools of thought in electrical diagnosis; using a test light or a voltmeter. A test light is a go-no go device. Connected to a circuit with voltage, the bulb will light; no voltage and it won't light. Pretty simple. However, there's no way to tell how much voltage is reaching the accessory with a test light. Automotive electrical accessories are designed to operate most efficiently with 12 volts. Anything less and the accessory (load) may not work as well or at all. If a circuit only has 10 available volts (instead of 12), the test light will still light which mistakenly indicates a functioning circuit. Not neccesarily so.
A voltmeter connects to a circuit in the same way as a test light and will tell you exactly how much voltage is reaching the load. Not getting 12? Trace back toward the source (battery) and find out where you lost 2 volts; usually a corroded, dirty or loose connection between source and load. You can also connect a voltmeter to measure the amount of voltage loss (voltage drop) in a particular segment of the circuit.
In addition, modern vehicles use several electronically-controlled systems. Many of these systems use a 5 volt signal to their sensor circuits. Probing these circuits with a 12 volt test light may/will fry the electronic control unit (expensive). Even an analog voltmeter can cause damage. A good digital voltmeter (VOM) can prevent this from happening.
For pinpointing the cause of a battery drain (parasitic current drain), I'd suggest connecting the ammeter (part of the VOM) in series with the positive battery cable, then follow his suggestions (pull fuse, etc.) for isolating the offending circuit.
Sherwood Lee
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