Published on January 2, 2012 by Boxpin
Remember your battery needs to be in good health before you can start this trouble shooting process.
Your going to need a multimeter that can read current draw. Basically you’re going to introduce your meter between your positive -or- negative battery post. This will cause any current the car is using to pass through your meter.
Do not attempt to start your car with your meter in place. Most meters can only handle 10 amps or less, your starter uses hundreds.
On a normal vehicle there are several electrical components that need voltage all the time. You will have a current draw regardless of anything being on. (For example, your radio memory or alarm system). The normal current draw should be around .01-.07 amps. If you are seeing higher than this you could lose your battery if your car sits for several days. Below you can see above average draw after recharging the battery.
In this case the car was pulling just shy of 1 amp or 8 tenths of one amp. Regardless the result of this is a dead battery after a few days. Find the circuit that the draw is coming from. To find the culprit begin pulling fuses from your fuse box. Pull them one at a time checking the meter then put the fuse back and move to the next. This will narrow down where the draw is coming from.
Eventually I found the fuse that was causing the draw. When pulled the draw went down to .02 amps which is right where I want it to be. I checked the fuse list to see what that fuse ran. It said dome light, courtesy light, etc. So I put the fuse back in and started looking. Eventually I found the rear tailgate had not been closed completely leaving the rear lamp on. We left for vacation during the day and returned during the day and did not see the lamp in the back. With the tailgate now closed I checked the meter and to my surprise there was still a current draw.
So I went through the process again. Again it was the same fuse. I checked the lights again and none were on. What else would light I thought. Visors and glove box came to mind so I checked. Turns out the glove box was also not closed enough to turn off the light within the glove box. With that corrected the draw was now down to .02 amps which is right where we want it.
Although this was a simple fix the principle behind these troubleshooting steps remains the same for more complex drain issues. The idea behind finding the culprits is to eliminate them from the system. For example if a diode pack goes out in your alternator you can end up with a current draw. Disconnect the Alternators main power and trigger lines then check your meter.