Battery drain
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Battery drain
I have a 1993 F150, 300 six cylinder, straight stick, that all of a sudden drains the battery to 8.5 volts over night. There are no options on the truck except air and a radio.
If I unhook the battery and read resistance between the cables, I get 54 ohms. That sounds like a pretty good draw to me. My question i guess is what is connected to the battery that is not switched with the ignition switch besides the alternator?
Any ideas what could cause this drain with the key off? Alternator? Ignition switch? Anything else?
Thanks for any help in advance.
If I unhook the battery and read resistance between the cables, I get 54 ohms. That sounds like a pretty good draw to me. My question i guess is what is connected to the battery that is not switched with the ignition switch besides the alternator?
Any ideas what could cause this drain with the key off? Alternator? Ignition switch? Anything else?
Thanks for any help in advance.
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Joined: Feb 2009
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From: So Cal/Mexico
I just answered the exact same question on some other forum-----turn your key off, disco the positive cable from the battery, put the black lead from your digital volt meter to the positive cable end and the red lead to the positive battery post. See if you have some voltage showing---like 2.3 volts or 4.1 volts...or whatever. Now then, as you stand there holding your meter and gazing at the readings, have your best friend pull out fuses from under the dash ONE BY ONE. When you see the volts suddenly drop on your meter, then you've just narrowed down the component(s) that is/are leaking. Very simple.
And check your starter also(battery connected)----red lead on the hot terminal on the starter, black lead to ground. If you're seeing anything more than say .1 volts (like 3 or 5 or 7), then you got problems there............
And check your starter also(battery connected)----red lead on the hot terminal on the starter, black lead to ground. If you're seeing anything more than say .1 volts (like 3 or 5 or 7), then you got problems there............
pedant
Joined: Jan 2008
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From: EXTREME southwest CT
If you have a second generation alternator (2G) the POS plug on the harness could be shorted internally as well.
So sometimes, unplugging the alternator won't diagnose this issue that is very common.
So sometimes, unplugging the alternator won't diagnose this issue that is very common.
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I just went out and tried all the fuses. It didn't make any difference, it always showed full voltage between the positive post and the positive cable.
Next I disconnected the battery and ran a resistance reading and got 6 ohms reading between the pos and neg cables.
Then I completely disconnected the alternator wires and I get a 5 Meg ohm reading. I cut the wires on the lower plug, as when it was new the instructions in the box said not to unplug it from the alternator or it would void the warranty, so I cut the splices.
I am leaning toward a bad alternator, but at 100.00 I would like to be sure before chucking out the cash. Is there anything else I can check?
Next I disconnected the battery and ran a resistance reading and got 6 ohms reading between the pos and neg cables.
Then I completely disconnected the alternator wires and I get a 5 Meg ohm reading. I cut the wires on the lower plug, as when it was new the instructions in the box said not to unplug it from the alternator or it would void the warranty, so I cut the splices.
I am leaning toward a bad alternator, but at 100.00 I would like to be sure before chucking out the cash. Is there anything else I can check?
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From: So Cal/Mexico
(sorry I'm not more helpful on the exact procedure to do this---just tossing out an idea for you to check).....
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Joined: Mar 2009
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From: Washington County, Penna
i agree, the alt went in my 250 and it would drain a brand new battery overnight, changed out to a new alt and now i can hold a perfect charge on that battery or my old crappy one that was in it, i took my alt to autozone and they tested it, failed miserably lol
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I took the alternator to the parts store and had it tested. It was completely shot. It even pulled the tester down trying to run it.
New one installed, everything seems to be fine. I checked the ohms reading between the cables with the new one installed, and it ran around 65 K ohms, if I remember right. I know it was a long ways from 6 ohms.
Thanks for all the help. This site is great.
New one installed, everything seems to be fine. I checked the ohms reading between the cables with the new one installed, and it ran around 65 K ohms, if I remember right. I know it was a long ways from 6 ohms.
Thanks for all the help. This site is great.
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
Anything drawing current in a 12V system (like radio memory) will show 12V.
...Still ok, but it should be in the milliamps range.
Ohm's law, it's simple Ohm's Law Calculators