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Old 08-28-2011, 12:48:58 PM   #1
AMP
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Negative Battery cable gets hot,no start

Hi,my 79 has an issue with batteries!There must be some kind of draw because the battery will go dead overnight if cables are left on it,only symptom ive noticed is a hot negative battery cable when i crank the engine.any thoughts?
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Old 08-28-2011, 12:54:41 PM   #2
Twisted_Metal
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Resistance = heat

You may have a poor ground connection.
It sounds like you have a drain somewhere else too.

Disconnect the positive cable from the battery terminal and use a test light to bridge the circuit.
Then... unplug the alternator and see if it goes out.

If it doesn't, pull fuses until you find the one using power. (Test light goes out.)
The clock only uses power in little spurts, you don't need to disconnect it to find your short.
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Old 08-28-2011, 12:55:13 PM   #3
grzewnicki
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Usually high resistance (poor connection) will cause wires to get hot. Check both ends for being tight and corrosion.
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Old 08-28-2011, 12:56:14 PM   #4
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Quote:
Originally Posted by grzewnicki
Usually high resistance (poor connection) will cause wires to get hot. Check both ends for being tight and corrosion.

yup, higher current and voltage drop...
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Old 08-28-2011, 01:40:36 PM   #5
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Quote:
Originally Posted by K5JMP
yup, higher current...

Nope. A resistance (in series here) where it doesn't belong reduces current.
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Old 08-28-2011, 01:43:51 PM   #6
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Quote:
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Nope. A resistance (in series here) where it doesn't belong reduces current.

which means it draws more current to do the job... which is what causes the heat.

26 yr electrical engineer.. but not worth argueing over..
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Old 08-28-2011, 02:00:18 PM   #7
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Time to go back to Ohm's Law and read what happens when resistance increases in a series circuit.
I=E/R
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Old 08-28-2011, 02:01:28 PM   #8
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whatever

power = current squared x resistance
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Old 08-28-2011, 02:03:29 PM   #9
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I just have a problem with nonsense presented as truth. Sorry.
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Old 08-28-2011, 02:09:44 PM   #10
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seems to me that you are considering a regulated power supply.. a battery ain't a regulated supply..


so let's just agree to disagree and move on.

clean all connections and then check the resistance of the cables with a VOM (possibly corrosion inside the connector itself)... that should steer the OP in the correct direction.
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Old 08-28-2011, 02:31:12 PM   #11
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i can confirm the battery cables are nice and tight,yet i have a draw that immediatly kills the battery.
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Old 08-28-2011, 03:35:49 PM   #12
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Disconnect the + battery cable. Put a 12 V test light from the + terminal to the (now disconnected) + battery cable. IF the test light lights, you have a short to ground. If it doesn't, then I don't know what to tell you.

Assuming that the test light does light up, start pulling fuses till it goes out. The one that turns the test light off is the bad circuit.

99.9% of the time, it turns out to be the dome light circuit. Sometimes it can be that the diode(s) in the alternator are leaking to ground.
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Old 08-28-2011, 03:37:58 PM   #13
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very interesting because my dome light dosnt work
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Old 08-28-2011, 08:44:30 PM   #14
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diconnected the dome light for now...fresh battery cranked for a sec then died with a hot battery cable.Cant seem to find the short to ground.
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Old 08-28-2011, 09:33:41 PM   #15
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Be sure to close the glove box door, i didn't and it took me a week to find the short
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