Truck Trend Garage: 2007 GMC Sierra Electrical Leak

Question: I have an electric leak on a 2007 GMC Sierra. The battery and alternator tested fine, but the battery goes dead every other time I let it sit overnight. Do you have any ideas why?   |   Current Events 2007 GMC Sierra Answer: The "electric leak" is referred to as a parasitic draw, meaning excessive current is being drawn from the battery with the key off, doors closed, lights out, etc. A certain amount of current draw is normal. A general rule of thumb is anything less than 50 milliamps is OK. Even for a top-notch technician, it can be very time-consuming to diagnose a parasitic draw. It involves measuring current flow with an ammeter while all systems are correctly put to sleep. That's when certain systems (such as the alarm) stay active for a designated period of time before they power down and reduce the current drawn from the battery. Sometimes a vehicle may have to sit dormant for more than an hour before it's officially asleep. Once a draw above 50 milliamps is confirmed, and obvious stuff has been eliminated, systems need to be disabled (remove fuses/disconnect connectors) one at a time to find the problem circuit. There's a specified trail of systems to disable in the service manual. You can check some basics, though: .