Dear Ole Mechanic;
My wife has a 1995 Chrysler, and the battery keeps running down overnight. After charging the battery again, a friend of mine disconnected the battery ground cable, put a meter between the battery and the ground cable, and it showed 12.6 Volts. We then pulled all the fuses, and the meter STILL showed 12.6 Volts. He said that there was a short circuit somewhere that was running the battery down, but didn’t know where it was because all the fuses were out. How can I find and fix this problem? I am not a “certified” mechanic, but I am fairly good under the Shade Tree.
Help! Shady Tree
PS: Soon to be up a tree if I don’t get my wife’s car fixed.
You are dealing with one of the problems that causes mechanics to become "ole mechanics," get gray hair, go bald from pulling their hair out, and resort to strong, adult beverages (and retire if they are lucky). Your friend has a good start on trouble shooting this problem, but it sounds like he needs a little more information and another step in his diagnostic procedure. I will get to that in a minute, but first things first.
Even if the battery is new, have it tested or test it yourself, as even a new battery can have a problem. That is why they have a warranty. If just one cell has an internal short, it can cause the battery to go dead. To test it yoursel,f you should charge the battery up, but do not connect it up to the Chrysler. Use caution, as the battery has a sulfuric acid solution in it. Let the battery sit for at least a day, and then connect it up, and see if it still has a charge. If it runs down without being hooked up, then it needs to be replaced.
OK, if the battery stays up, then it is time for the trouble shooting step that your friend did not get to. With just the battery ground disconnected, get a 2 ½ amp fuse, and use it and a short length of wire to ground the battery. Be sure that everything is shut off, and close the door (or the dome light will be on), and disconnect the under hood light too--or better yet, pull all the fuses again. If the 2 ½ amp fuse does not burn out or blow, then the 12.6 Volts that your friend found at the ground cable was probably the voltage needed for the various computer and component memories. It is called “Keep Alive” power and is what keeps the clock running, the radio buttons on the stations that you set them on, and retains the “learned” memory part of the engine’s fuel-injection computer. You could use a sensitive amp meter in place of the fuse, if the fuse doesn’t blow. It will usually show a small surge of amps--usually less than 2 amps when the battery is first grounded through the meter--and then taper or drop off to less than 1 amp of current draw. If the current draw is less than 1 amp or the 2 ½ amp fuse does not blow, then it should take three to four weeks for the clock, radio and computers to drain the battery down to the point where it will not start the Chrysler. To give an example of how small the battery drain for computer is, a small bulb like a glove box light left on can drain a battery in four to seven days. OK, so much for what is going on if the fuse doesn't blow.
If the fuse blows immediately when you ground the battery, then it is time to double check all the fuses--both under the dash and under the hood--to make sure that they were all pulled. Unfortunately (or maybe fortunately,) the smoke test does not seem to be working with this Chrysler. The smoke test involves hooking up the battery and looking around to see where the smoke is coming from. If all of the fuses were pulled, then it is time to check the items that do NOT have fuses. Fortunately, there are not too many of them. The first is the alternator. It has a hot wire directly to the battery, and if one of the internal diodes has gone bad, the alternator will still charge, but it will also discharge the battery when the engine is not running. To check it, disconnect the big wire--usually Red--from the back or side of the alternator. Move or tape the wire so that it can not touch anything, and try grounding the battery again with yet another 2 ½ amp fuse. If it does not blow, then it is time to replace the alternator, as the diodes are not usually a replaceable item. If the Chrysler has a digital dash, I hope that the alternator is OK, because the last time I replaced one it cost over $250--just for the alternator.
If the fuse does blow, then it is time to check the ignition switch. No, you do not need to pull the steering wheel, as the key is located under the wheel in a convenient location to lock the wheel and connect to a long rod that connects to the switch. The switch is on top of the steering column under the dash. Unplug the wiring connector from the switch, and try another 2 ½ amp fuse. If the fuse still blows, then unplug the wiring from the light switch, and try still another fuse. If that fuse blows, then it is time to disconnect the starter solenoid--and then the starter. That is the really big cable type wire that usually disappears down under the engine. I hope that you got a box of 2 ½ amp fuses, because with the starter disconnected, it is time to ground the battery again.
If it still blows, then it is time to start following wires, buying some “Just For Men” hair dye, getting a hair-piece, or heading to the refrigerator for several adult beverages. Better yet, you can take those beverages and some $ and pay a visit to,--you guessed it--your favorite mechanic.
Herr Professor Nuzanbolts (who is balding, gray, retired and headed for the frig)