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Diagnosing an electrical power drain

This isn't DSM specific, but as DSMs are getting older, these problems are becoming more common.

Difficulty Level(1-10, 1=easy): 5

Required tools:

test light
multimeter (optional)

1. Be sure the ignition lock is in the "OFF" position, all lights are off, and all doors are closed. Be sure that nothing is plugged into the lighter, drawing power.

2. Remove the negative battery terminal (if your car has an underhood light, disconnect it).

3a. Place the test light between the battery and the cable. The light should not illuminate. If it does, you have a draw somewhere. To test your connection, leave the test light hooked up, and open a door. The light should get very bright, this is normal. Or the meter should show a large amp draw.

3b. Place your multimeter on the lowest amp setting. Place the test leads on the battery and the cable (it doesn't matter which one goes where). 30-40 mA is an acceptable draw (to power the ECU memory, radio memeory, etc.). Any more than that is unacceptable, and will kill the battery after a short period of time.

4. If you do have a draw, leave the test light or meter hooked up. Go to the fuse box. You'll have to remove the courtesy light fuse, or else the open door will keep the test light illuminated/meter showing a draw. If you remove the courtesy fuse, and the light goes out, the draw was in that circuit, so check all courtesy lights, door switches, etc. If it stays on, the draw is still present, so start pulling and replacing fuses one by one. When the test light goes out, you've found the circuit that has the draw. You'll need to check all the parts/wires on that circuit for a broken wire or shorted component. Usually, it turns out to be something simple and you'll find it right away. If not, you'll need to consult a manual to see the wiring diagrams and be able to trace all the wires to check them for a short.

If you are still unable to find the short after consulting a diagram, there are short finding tools available. You can also make your own (I'll post instructions for making and using the tool later).

If it turns out that you don't have short, and you're battery is still dieing often, the battery can be no good, or you're alternator could be bad. To check the battery, you need to put a load on it. This can be done at most Pep Boys, Auto Zones, etc.

To check the alternator, hook up your mulitmeter (on the DC voltage setting) to the positive and negative battery terminals. With the car running, you should be seeing at least 13 volts (which is very low). 14 volts is good. Turn on the headlights and wipers, the voltage should still stay above 13, if not, replace the alternator.
 
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