Short circuit or bad battery? Testing for car electrical problems
If the battery is dead when the car has been left alone for a day or more, and no lights were left on, the problem could be in the wiring or the battery itself.
Tannon Weber wrote:
Disconnect the negative cable from the battery and bridge the gap with a multimeter, looking at the DC amps reading. Assuming that there aren't any components that run while the car is off (security system and the like) you shouldn't get much in the way of a reading. If you do, something is discharging, and it could be a wiring fault or a device that has failed.
Some Chryslers (including Dodge Rams) have a circuit that cuts out one set of lamps when the fog lights are enabled, so there could be some kind of fault there.
Bill added: “I have used the multimeter on the negative terminal as suggested earlier, along with pulling one fuse at a time. That way, you narrow the suspect circuit down quickly.”
Bob Lincoln clarified: “Disconnect the negative cable and measure the current draw between the negative cable and negative post, using an ammeter that has a 10 amp range. If there is a noticeable draw, then pull one fuse at a time until the draw goes away. Now you know what circuit is causing it. Look in the owner's manual, to find which fuse number it is and what functions are on it. Look at those devices one at a time until you find the exact cause. This may take a little time, but is guaranteed.”
Allan C. wrote:
Next time the vehicle will sit for 3 - 4 days without being driven, remove one battery cable. After 3 - 4 days of non-use, reattach the battery cable (make sure the connection on battery post and cable terminal are clean). If the battery spins the starter vigorously then you know there is a parasitic drain of excess current which is depleting the battery. If the battery is weak and will not operate the starter, the battery has an internal problem.
Common sources of excessive parasitic drain include courtesy lamps which do not turn off after a door, the trunk, or the glove box door is closed.
Imperial Crown added: “If you have the courtesy lights on the rear view mirror, make sure that they are off. The switches are easy to bump on and the lights are hard to notice in daylight.”
John Wood added: “I recently had an issue with a multi-changer CD player that was doing this. I unplugged it from the radio and that resolved it. My drain went from about 60 milliamps to 5 milliamps.”
Gary S. wrote:
It could be something in the seat control module (inside the center console) or its associated wiring.
The shoulder belts have a solenoid inside the seat back that is energized when the doors open and the ignition is off. This allows the belt to be extracted and latched before the ignition is turned on, but turns them off when the car is parked. If the solenoids remain hot, the battery will drain in a couple of days.
Put the top down, or open the windows and let it sit for a while, (some models have a time delay in the circuit) and then try to extract the belt without opening the door. It will not extract if the solenoids don't have power. Another way to do it is to unplug the harness under both seats and let the car sit for the time it's taking the battery to run down.
Gary S. added:
[If it has been isolated to the seat belt module,] you could disconnect both harnesses under the seats and let the car sit for the time it usually takes for the battery to run down. If the battery stays charged, that would isolate it to the seats, but wouldn't tell you if it was a problem in the seat control module or in one of the seats. You could disconnect each side individually and let it sit, and that would isolate it if the seat itself is a problem, but it could also mean a problem with the module.
If you have a helper, you could have them uplug each seat while you put your ear against the seat, just below where the belt enters the seat. As the harness is disconnected, you should be able to hear the solenoid release. I could hear them on mine.
You could start pulling fuses, as others suggested, but you still have time-delay circuits to contend with when troubleshooting. The dealer probably has a diagnostic test that would find it quickly, but we all know how expensive it is to take it there for repairs.
Also see checking computer codes