Be sure to remove any cables that may be plugged into your vehicle, like a GPS unit or phone charger, as well.
Many car batteries are 12. 6 volts. You can check the power with a multimeter to ensure the battery is fully charged. If your battery is old or damaged or isn’t reading 12. 6 volts when fully charged, you may want to replace it before moving on.
Be sure to use the negative, not the positive, cable to test for the draw to prevent electrical shorts! Generally, a 10-mm open-ended wrench is the tool you’ll need to remove the cable.
Choose a digital meter than can read up to 20 amps and down to 200 milliamps. [6] X Research source
You can use plastic clamps to secure the leads in place so your hands are free and the meter continues to operate.
Once you’ve worked through all of the fuses in the fuse box under the hood, check the fuses in the fuse box(es) under the dash. It’s best if you have a friend help you with this so one person can pull fuses while the other person watches the reading on the multimeter. If you don’t have anyone to help, prop the meter against the windshield so you can read it from inside the vehicle.
Usually, you can find digital copies of the manual and wiring diagrams online.
For instance, say the offending fuse controls the power antenna as well as the radio. Unplug the radio and see if the draw goes away. If it doesn’t, unplug the antenna and watch for the reading on the multimeter to drop.
You may be able to simply flip a switch into the “off” position to eliminate the draw, or you might be facing a more complex problem, such as an issue with a wiring harness.
