Large Battery Drain
 

Did a search but didn't come up with anything.

'93 Manual has been losing the charge on the battery. We put in a new battery and within a day the battery is dead. The car is garaged and not driven in that time frame.

None of the interior lights are on. What kind of short or electrical problem could drain the battery that fast. I'm looking for a priority list on which fuses to pull first. Would rather not meter every fuse at random and find the last one checked was the culprit.

Ideas/suggestions? Thanks in advance.

Check to see if the rear wiper motor is stuck on. Mine froze on the 84. It's not in the fuse panel, which made it hard to track down. It would drain the car quickly. For a quick check touch it and see if it's warm

I believe you should be able to do a voltage drop check. Get your voltmeter out and you should be able to probe the fuses without removing them. There is a small opening in the back of the fuses where you should be able to fit the probes. Anything with voltage on it means that something is consuming power in the circuit. Took me about 15 minutes by this method to probe every fuse and to find that the cause of my drain was the glovebox light. It was staying on due to a misadjusted glove box door. Much easier process than just making guesses. Hope this helps. Joe

What Joe says is a great way to track down a current drain through a fused circuit. It is fast and very sensitive. Trymeasxuring the voltage drop for the interior lights with the door switch open and closed. I thinks it a few milivolts. If you see that where it shouldn't be, that's your culprit.
Good luck,
Dave

Randy, One of my cars had a battery drain and I found that it was stuck window switches. I had raised the windows and the motor was still active, but obviously the window was going nowhere. I finally just detected the faint hum. I tapped the window switch and it stopped. I'm in line for the illuminated stuff from Hans and Paul.

Thank you for your suggestions. Not having to remove the fuses would save a lot of time.

I am confused about measuring at the fuse. Won't there be voltage at every fuse when you connect the probes to each side? How do you measure "voltage drop"? I thought amperes measured current flow. As you can tell, my electrical knowledge is limited. But I do have a mystery battery draw that I am trying to locate.

You will be doing this with the ignition off so there should not be power going to anything meaning that any voltage that you find will be a draw. The only place that you have to be careful is with the red lights in the doors that may be illuminated with the doors open and maybe the clock, but you should be able to figure this out by looking at the fuses. Resistance, Amps, and Voltage are all interrelated if you look at the mathematical formulas for figuring out each, unfortunately I can't remember each one off the top of my head. With your ignition switched off and making sure that all other lights are off, set you voltmeter to volts, and put the positive and negative probes of the meter to the back of the fuse terminals that you want to check. The reading should be zero, if any voltage is present find out what that fuse powers and you can unplug each component until it drops to zero. That is unless it is in the wiring. In that case you will be looking for loose, broken, melted wires in the harness. Hope this helps. Joe

E = IR

A fuse is a very low R so unless you have a VERY high I you will also have a very low E.

A bit of clarification...

Quite a few of the fuses will normally have power on them with the ignition switch off. The only thing that checking for voltage on the fuses will do is to tell you which circuits are hot with the switch off. While there is a good chance that the current drain will be on one of those circuits, it is not certain that it will be, as there are quite a few constantly-hot circuits that are not even fused.

To drain a charged battery in a day without letting out the magic smoke, you must have a drain that is going thru a reasonable resistance. A hard short-circuit to ground will cause smoke or a blown fuse in a very short time. The most likely cause for your problem is a device that is on when it shouldn't be. Possible candidates include the already-mentioned window motor (check the switches to make sure that they aren't hanging on the plastic), a sticking relay, a faulty interior light switch, a faulty diode in the alternator, etc., etc.

One of the first things to check - do the interior lights work exactly as designed? That is, do they go on when a door or the hatch is opened, and go off shortly after it is closed? If not, that is the first place to start looking.

Is there an after-market audio amp installed? If so, it might be staying turned on.

Is there an after-market alarm system? If so, check it for current drain.

Let us know what you find.

Sorry this is not a good technique - there are many fuses that have voltage on them all the time - so what...

Alan

There really is voltage to many fuses all the time... there really are many circuits that don't go though the fuse panel and there really are some circuicts that don't have any fuses at all.

Measuring across active circuit fuses with a voltmeter coulds work - but most cheap voltmeters will look like they are reading small voltages even when they aren't ...

It really isn't that simple. There are plenty of descriptions of how to track down parasitic current draw on Rennlist - just do a thorough search

Alan

You are right, Alan as usual. However this technique is very fast and you may find that you have a voltage drop on a seat heater or a rear defroster, and you may solve a problem quickly. With the ignition off, you should have power to clock, radio, ECU's and just a few other items. By power, I mean items that are actually consuming power, thus creating a voltage drop. This will not help on infused circuits and of course you need a good digital voltmeter.

Alright while this isn't the end all method for finding draws it is extremely simple and quick. While there will be power to some things with the ignition off it would point you to an obvious draw, hence me finding the glove box door being misadjusted. From what i remember I used a Craftsman voltmeter that was purchased for $15 and it read 0.00 volts on most of the fuses, but not the ones with power going to them with the ignition off. Will this method find all draws? No. Will it find most obvious ones with the use of a little common sense? I would have to say generally yes. Joe

What did it read on the one feeding the GB light? I would guess quite low. Like 20 mV or less?