The Stovebolt Site Forums The Shop Area The Electrical Bay Weird battery drain

First some background. 12v conversion, brand new battery, fresh install of new EZ Wiring harness, new alternator.

So I finished my wiring harnes job a few months ago, truck was fine since, ran good and everything worked. About a week ago my battery was dead and would not take a charge, so I got a new battery. Put the new battery in, truck fired right up and ran great. Next day, the truck won't start and battery reads less than 2 volts. My cheap $20 charger wouldn't charge it, so I connected the battery to the wife's Durango's battery with it running for a few minutes and that charged it up. Put the battery back in the truck and it starts up and runs fine.

What could cause a brand new fully charged battery to go from 12.5v to less than 2 volts overnight? I double checked and I did not leave the headlights or anything on. Besides, even if I had left the lights on, I don't think it would drain the battery completely like that. The truck was off and the key wasn't in the ignition.

So, I checked with an Ohm meter, and nothing is pulling any current except for the guages. When the truck is off and the key is out, there is a small amount of resistance in the Ohm meter.

I did this test by connecting a an ohm meter across the battery, which showed a little resistance, like 100 Ohms or so. Then I removed each fuse until it showed an open circuit.

So then I noticed, which I never noticed before, is that with the truck off and the key out, the gauges still show a reading. Not the lights, but the gauges themselves. The needle still reads the temp, voltage and fuel level. That seems starnge to me, I don't think it's supposed to be that way.

So first, are the gauges supposed to still get power even when the ignition is off? (They're brand new VDO electric gauges).

And second, could the gauges being on overnight be the reason for the battery to drain down to 1 volt?


Thanks!

I don't know what ignition switch you have, but some of them have a terminal that stays hot all the time. When I first put in the aftermarket turn signal on my '51, I connected the signals to this terminal so that I could run the flashers with the ignition off. Bad Idea. I ran the battery down numerous times, because either I left a blinker on, or eventually the peanut light in the signal switch would run the battery down if I didn't drive for a few weeks.

So you may have the accessory wire of the harness connected so it will power you gauges all the time. This will drain your battery. I would change this if I were you.

Also, your new battery might have not had a full charge, or might have been "old" on the shelf. I would check the date code on the battery, and if it is not recently manufactured, I would take it back and ask for a new one.

Kurt

Forgot to mention that it has a 69/70' GM column, and the harness already had the connectors pre-wired for the column, so all I had to do was plug it in.

Ohmmeters have their own power source, and should never be connected to any circuit with voltage on it. Connecting one across a battery would either smoke the meter, if it's an old analog type, or make a digital meter read an overload. Are you sure that's what you're using? If so, your readings are meaningless. Your gauges should not be powered up unless the ignition switch is in the run position, so they're obviously wired incorrectly.

Try disconnecting a battery cable, and use a digital multimeter with a 0-10 amp setting on the dial. Connect one meter lead to the battery post, and the other lead to the cable you just removed. The meter should show less than 1 amp of current draw, the smaller the better. Only things like a sound sysytem or maybe a clock with a "keep alive" memory need an unswitched battery voltage connection, and that circuit usually draws only a fraction of one amp. If the parasitic current drain is one amp or more, start disconnecting circuits one at a time until you find the source of the drain, and fix it.
Jerry

I have a digital multi-meter, but the it only has a 2mA, 20mA and 200mA scale. I don't think it goes above 1 amp.

Another option would be to use an ice pick type 12 volt test light, and connect it in series with the battery cable. If there's enough current draw to make the light burn, or even glow more than dimly, you've got enough parasitic drain to draw the battery down. One common cause of an overnight battery discharge is the rectifier in the alternator. Try disconnecting the big charging wire from the alternator and see if the overnight draw-down stops. Don't let the exposed ring terminal touch anything- - - -it's best to insulate it with tape.
Jerry