Hi,
Please excuse the noob question, but my battery is mysteriously draining. If I don't drive my car (89 240sx) for a few days, then the battery dies. I don't believe my alternator has gone bad, because if the engine runs, then the battery gets charged.
The only other thing I could think of would be bad wiring in my DIY alarm install job. However, I installed my alarm more than a year ago, but this problem only came up recently. Since the install, I've also gotten a smog check, as well as a clutch replacement, but nothing really seems to clearly be the source of this problem.
I'm wondering what's the best way to go about looking for a drain on the battery. I'm a complete amateur when it comes to using a multimeter, so please be as thorouogh as possible. Any tips on where to start, what to look for would be much appreciated. Thanks!
BTW, this has happened with a brand new battery. And my alarm is the rsx 3.5
You can disconnect the neg batt cable, and place a test light in between the cable end, and batt terminal, watch licht as you pull every fuse. when the light goes off, or dratically dim when you pull the fuse, it means the draw is on that circuit. this saves me a lot of time, neat trick i think.
You mentioned that the Alternator charges the battery ok; but the alternator
can discharge the battery if an internal diode is shorted, allowing current
backflow when it is not operating. Disconnect the alternator wire and
put a tailight bulb in series with it to the terminal: if it lights there is a
current backflow thru the alternator.
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loneagle
Don't use a test light. That method only works on cars old enough to be in the junk yard. You MUST use a digital volt meter which is capable of at least a 10 amp current draw. To begin, first set your meter to a DC voltage scale and measure the battery's votage at rest. Put your red probe on the red positive lead and your black lead to the negative post of the battery. Your battery should measure 12 volts or higher. If it doesn't then you must first charge your battery. If the battery won't stay over 12 volts after charging it, then replace the battery. Secondly, start the vehicle and measure the voltage at the battery again. The reading should be about 13 to 14 volts. If it is, then your alternator is charging the battery. If it isn't, then your alt. needs repairing. Set your meter on its DC amperage scale and move your meter's test leads to the correct ports in the meter. Check your owner's manual for the meter if you have one. With the ignition off, disconnect the negative battery terminal. Close all doors on the car. Place one meter lead on the negative battery post and the other attach to the negative battery cable. You should get a reading on your meter. To confirm everything is testing correctly, open a door and the reading on the meter should rise and the interior light should come on. Make sure the dome light switch is set to activate the light if the door is opened. Close the door and watch the meter for at least 20 to 30 minutes. The reading should not be above 50 ma. Depending on your meter the displayed number may be 0.05 amps which is 50 ma. This is the accepted maximum limit a car should draw at rest. if the draw is higher, then start pulling fuses out of every fuse box, one at a time to identify which one causes the meter reading to drop. Post your results for members to help.
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sparky