Which diagnostic tool should be used for troubleshooting a slow drain on the battery?

Using an ammeter is the most appropriate choice for troubleshooting a slow drain on the battery. An ammeter measures the electrical current flowing through a circuit, which is critical when diagnosing battery drain issues.

When trying to identify a slow drain, you would connect the ammeter in series with the battery or the affected circuit. This allows you to see how much current is being drawn from the battery when the vehicle is off. A higher current reading than normal would indicate that there is a parasitic draw, helping you pinpoint the source of the issue.

In contrast, tools like ohmmeters measure resistance in a circuit, voltmeters measure voltage levels, and test lights indicate the presence of voltage but do not measure current flow directly. While these tools can provide useful information in different diagnostic situations, they are not specifically designed to quantify current draw, making them less effective for this specific problem of identifying a slow battery drain.