I have an old (1990) Acura Legend.
- For the past few years, the battery dies even during mild winters, or after 3-4 days of inactivity.
- I have changed battery 2 times but the problem remains.
- Mechanic told me alternator, etc all checks out OK.
- Said there may be "short" somewhere he is not able to find.
- Special mechanic is asking several hundred dollars working for hours to look for the "short" with no guarantee he fill find it.

Questions:
- What is "short" in the car electrical system?
- How to know if there is a "short"?
- What are some common things that create the "short"?
- What are some simple things I can do to find out where exactly is the "short"?

Thank you for the help.

Kris
01/06/2008

It may take some time to find but it should not cost anywhere near that much. An amp meter is the tool of choice. The meter will go inline (in series) with one of the battery cables. Disconnect the battery cable at the start of your testing (after windows are down), insert meter between battery and cable, insure the meter moves in the positive direction or reverse red and black test leads. Leave the leads hooked up at all times during testing, nothing big will be able to be turned on like lights, it may blow the fuse in the meter so be prepared if the meter quits working, start on the 10 amp scale and switch down to lower setting as tests allow. Try to get the needle as high as possible on the scale (by lowering scale settings).

Lower the drivers window so that the door does not need to be opened, leave the hood open to gain access to the underhood fuses. Once the Amp meter is hooked up it may take several minutes for the computer or other black boxes to "Go To Sleep", then the tests can start.

Baseline, once the car has gone to sleep, take an Amp reading, I believe that you will eventually be looking for less that 50ma (milliamps) by the time you find and fix the problem. Start by pulling the larger fuses, forgot to mention that a complete vehicle wire diagram will also come in very handy.

When a certain fuse is pulled you will follow the schematic down the chain to smaller fuses possibly under the hood or under the dash, when finding a faulty circuit by pulling a smaller fuse you are getting close. Do not open the door to get in the car, climb through the window. Opening the door will wake up the car again.

Let us know your understanding of this explanation so far and what you have done to test so far and some findings. Radio and dome light and sometimes brake lights are problems. Corrosion somewhere may also be causing a small parasitic drain to ground not being a bad enough short to blow the fuse. Maybe water intrusion to the back side of the fuse box, BTDT.

Battery Drain

Parasitic battery drain is the cumulative load produced by electrical devices (e.g. ECMs, clocks, security alarms, and radio presets), when the ignition is turned off. These items continue to operate, when the ignition has been switched off, and are becoming an ever increasing problem. Normal parasitic loads are below 75 milliamps (.075 amps). When parasitic load is greater than 75 milliamps, batteries will drain even faster. Glove box, trunk, and under hood lights that do not automatically turn off when the door is closed, or shorted alternator diodes, are common offenders. Cooling fans, power seat belt retractors, radios and dome lights left on, alarm systems, and electric car antennas can also cause batteries to drain overnight. Leaving headlights on will usually discharge a fully charged car battery, with 90 minutes of reserve capacity (36 amp hours), in a couple of hours.

Two methods are used to test for parasitic load (engine off, under hood light disconnected, accessories off, and vehicle doors closed):

1. The basic approach is to connect a 12-volt bulb across the positive and negative battery terminals to test the bulb and battery. If it glows brightly, remove the negative battery cable and connect the bulb in series between the negative battery cable connector and the negative battery terminal. If the bulb continues to glow brightly, start removing fuses or connections to the positive battery, one-at-a-time, until the offending electrical component is identified by the bulb dimming.

2. The best approach is to use a DC ammeter, connected in series between the negative battery cable connector and the negative battery terminal, or a clamp meter (set to DC amps), clamped around the negative battery cable. Starting with the highest scale (or set multimeter to auto range), determine current load. If load is above 75 milliamps, after the initial surge, start removing fuses or connections to the positive battery post, one-at-a-time, until the offending electrical component is identified by the parasitic load dropping to 75 milliamps.

In my case I found the problem in the recently (professionally? ) added CD player, could be a place to start if you've had anyone work on your car. Good luck

I know you said you checked the alternator but I have the same car and had the same problem! I replaced the alternator still did it then I cut back the cables on the battery terminal and replaced the connectors no problem since. Good luck

I'm having the same problem with a legend I just bought at first I thought the car was a piece of ****, Got stuck on the highway 15 min after I bought it bought a battery at a local junk yard and still needed a jump. Brought it home to start working on it.Changed the Alternator fuse in the engine bay then I bought battery terminals same thing Bought the alternator just replaced it and the same problem occurred. I'm thinking it may be faulty wiring, maybe the wire harness.