Electrical troubleshooting procedure
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Electrical troubleshooting procedure
I have read three different post about dead batteries and folks checking voltage drops. This is NOT how to determine if you have a short! Current drawn from your battery when the car is off is called parasitic loss. The way to check for this current draw is by using a multimeter set to measure DC amperes. You must reconfigure leads on the multimeter to do this. Once you configure your meter to measure amperes, you disconnect the negative battery terminal and place the positive lead on the negative battery post and the negative lead on the negative battery cable. You are now measuring current! On most cars, reading more than 20 milliamps is an issue. Maybe a Mercedes expert can comment on draw you should expect. I hear 100 milliamps is normal on these cars - not sure. If you are reading high current numbers with the car off, you have a problem. You then start pulling fuses until that draw stops. You then have isolated the circuit where the issue exists. Then you have to find where in the circuit there is an issue. Door, hood and trunk lamp switches are common areas that cause parasitic current draw. The switches remain on when the door etc is closed. Now, Mercedes cars have issues sometimes when the battery is disconnected, so be sure to look into that before you begin. Hope this helps!
