In the morning, you get behind the wheel, turn the ignition key to fire up your engine and all you get is a moaning sound or no sound at all. Electricity leakage or battery drain can slowly discharge the battery in your vehicle after sitting in your driveway for a few hours. A door that fails to close tightly, an electrical short or a bad connection may keep a light bulb or an accessory on and gradually consume battery power. Find the problem and restore the electrical system in your vehicle with a few tests you can perform at home.
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Things you need
- Digital ammeter
- Fuse puller
- Vehicle service manual, if necessary
Pop your vehicle's hood open and disconnect the ground (black) battery cable with a wrench.
Get your digital ammeter out of the toolbox. Connect the ammeter black probe to the battery post you just disconnected and the red probe to the terminal of the battery cable.
Remove the light bulb from under the hood, if your vehicle is equipped with it. Close the boot and the car doors as well. Make sure all accessories are off.
Turn on your ammeter. The readout should register 0 amps, or about 10 ma (milliamps). If the readout registers above this figure, it is possible you have an abnormal drain in the electrical system.
Ask an assistant to remove the light bulb from the boot, close the boot and then replace the light bulb. Do the same with the glove box light bulb. If removing one of these light bulbs causes the ammeter to read zero, that light bulb is staying on after closing the boot lid or glove box. Make sure the boot or glove box is closing tight by pushing on the light bulb switch, and then check the light bulb socket for a short.
Close the boot and glove box tightly and make sure all accessories are turned off. Ask an assistant to pull a fuse from the fuse box from under the dashboard using fuse puller.
Read the display on your ammeter. If the meter readout remains the same, ask your assistant to replace the fuse and pull another fuse.
Repeat until the readout in your meter goes to 0 when your assistant pulls one of the fuses. The circuit that fuse protects is the source of the electrical leakage.
Check the wiring diagram for that circuit in the vehicle service manual for your particular vehicle make and model. This diagram will tell you the components and connections on this circuit so that you can perform pinpoint tests to locate the short circuit or bad connection causing the leak in the circuit. Or, if you prefer, take your vehicle to an automotive electrical shop and have them fix the problem.
Disconnect the electrical wires from the starter solenoid -- the small cylinder on top of the starter motor -- if none of the fuses that you removed from the fuse boxed caused your ammeter to read 0. If disconnecting the starter solenoid causes the ammeter to go to 0 amps, you have an electrical short in the solenoid or the wires connecting to the solenoid.
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