Batery Drain Diagnosis

Batery Drain Diagnosis

>I have a 82 928 have had the alternator replaced 2 times within 6 months.
>If I don't drive the car in 3-5 days, something drains the battery (which is new)
>and it won't start. Can you possibly give me somewhere to look for this irritating

Do you know how to work a multimeter? If not, this sounds like a good time to learn. You can buy a decent digital multimeter at Radio Shack for less than $25. It will allow you to measure battery voltage and current drain. Please be aware that as you switch the meter between the two types of measurements that you will most likely need to change the positions where you plug the test probes into the meter. It is a common error (and one which I have done many a time) to forget that you have the meter configured to measure Amps (current) and then you try to make a Voltage measurement. That causes a fuse to blow in the meter!

Configure the meter to measure current, disconnect your battery ground strap, attach one probe of the meter to the ground strap and the other probe to chassis ground. Check the current draw and compare it to the following Tip:


If the current drain is excessive, now comes the hard part: finding the source of the short.

It could be something like the interior dome light. See:



One way to locate the short circuit would be to remove and replace each fuse one at a time, watching the current draw to see which fuse causes a significant drop in the meter reading. This will allow you to isolate the circuit that has the problem.

Let me know what you find out.

Good Luck,

+Greg Nichols
Alexandria, Virginia
'87 928S4, 5-speed, Venice Blue Metallic

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