What kind of meter can test amperage draw?

jayp

This is car related but it's electrical. I have a 2004 Ford F350 with a weird power drain. When the truck is off, key out & no lights on the battery is being drained somehow.

I went to the auto parts store and the guy there had a battery tester that showed there was an approx 10.5 amp drain when the truck was off. I figured if I could buy some meter that would show me what kind of draw what coming out of the battery, I could go through and pull all the fuses under the dash until it stops to isolate the circuit. There must be a short somewhere or something that's not cutting off. 10.5 amps is huge though! Does a multimeter show this?

oleguy74

yes.set to amps,if range is enough.pull pos or neg lead,put meter in series.or just get a test lite and do same test.remove fuses til light goes out.ign sw could be bad also...

mpoulton

10.5A is enough power that you should be able to see, hear, or feel whatever is using it. That could be the fuel pump (though they don't usually draw quite that much), window defroster, seat heaters, lights, cigarette lighter (hope that's not on continuously!), or something else of that magnitude. If you poke around carefully you can probably figure out what's still running.

AllanJ

Most multimeters will measure amperes but only up to two or three. So you may not connect it to your truck suspected of drawing 10 amps because that will burn out the meter.

They make stand alone ammeters that measure larger amounts of current.

To do an in-line amperes reading, disconnect the wire suspected of drawing the amps (here, remove one cable from the battery), then connect one meter probe to the wire end and the other meter probe to the place the wire was connected to. (Plus meter probe to the side closest to the positive terminal of the battery for example if you disconnected the negative battery wire, connect the plus meter probe to the wire and the minus meter probe to the battery terminal.)

The jaws of a clamp on ammeter are not meter probes. Leave all wires connected when placing the jaws around one of the wires.

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davido30093

Assuming that you have made the normal checks and cannot find anything left on, the first thing that I would do is disconnect the alternator and then test for current draw as that is the most common cause of your symptom. If it is not the alternator, then, with a multimeter (ampmeter) in series with the battery cable, begin pulling fuses until you find the current draw.

joed

Most amp setting on multimeters only go up to 10 amps. You are going to need specialty meter that reads over 10 amps.

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davido30093

He said that the current draw is supposedly 10.5 amps. Any good "10 amp" meter should not be hurt by that. If I was going to leave it hooked up for a long time, I would probably put a resistor in series to reduce the draw some. All we are looking for is a go/nogo on the heavy draw. I still think that it is most likely a diode in the alternator leaking reverse current.

Pull a fuse, connect the lead of the meter to see if the draw is there. If so, disconnect meter, pull a different fuse, repeat.