Drain Test

Check for current drains on the battery (10655) in excess of 100 milliamps with all the electrical accessories OFF, and the vehicle at rest. Current drains can be tested one of three ways:

Connect a 12-volt test lamp in series with battery positive terminal. If lamp glows, then a drain exists.
Use an in-line ammeter between the battery positive or negative post and its respective cable.
Use a clamp-on current probe to the battery positive or negative cable. Make sure that the probe is properly calibrated to prevent false readings.

Typically, a drain of approximately one amp can be attributed to an underhood lamp, glove compartment lamp, or luggage compartment lamp staying on continually. Other component failures or wiring shorts may be located by selectively pulling fuses or disconnecting fuse links to pinpoint the location of the current drain. When the current drain is found, the test lamp will go out or the meter reading will fall to an acceptable level. If the short is still not located, after checking all the fuses and fuse links, the drain may be due to the generator/ voltage regulator (VR) (10316). Disconnect the generator output wire from the output stud and the generator regulator connector. If this eliminates the drain, check the charging system to locate the concern.

NOTE: A voltmeter is sometimes used for this test but it will react to a very small normal drain caused by "always-on" electronic systems such as starter interlock, anti-theft alarm, illuminated entry, etc, which cause no concern. The test lamp shows only drains which are large enough to cause a concern.

NOTE: For vehicles with electronic instrument cluster or message center, when the Message Center is initially powered up (after a battery disconnect), the Message Center "computer" may be energized for as long as one minute causing a 0.25 amp current draw before returning to the normal 0.010-0.012 amp current draw. Therefore, it is important to allow at least one minute to pass (after ammeter hookup) before observing any current measurements.