battery dies..
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Joined: Jul 2002
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From: torrance
Take a 12v test light. Disconnect your negative cable. Connect one end of test light lead to the cable and the other lead to the negative post. If you get a light (dim or otherwise) you have a parasitic drain. Could be your radio, clock or some other device drawing electricity.
If you have a light, then start disconnecting fuses until the light goes out as you have found the culprit. Check the wiring at that location for a short or bad groung.
If you have a volt meter in the cab of your truck, make sure it is at zero when you turn the key off. In my 86, if you don't jiggle it after the engine is turned off it will sometimes stay in a position where I get juice to the gauge.
Not the gauges fault but the fault of the ignition switch.
Chuck
If you have a light, then start disconnecting fuses until the light goes out as you have found the culprit. Check the wiring at that location for a short or bad groung.
If you have a volt meter in the cab of your truck, make sure it is at zero when you turn the key off. In my 86, if you don't jiggle it after the engine is turned off it will sometimes stay in a position where I get juice to the gauge.
Not the gauges fault but the fault of the ignition switch.
Chuck
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Joined: Dec 2003
Posts: 6,658
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From: "Islander"
Sounds like one or more bad diodes in the alternator or the regulator going south. It would take days for a light on to drain a battery unless the battery didn't have much of a reserve in the first place. Have you checked the battery as more demands will be asked of it during cold weather?
Last edited by "Beemer Nut"; Nov 19, 2007 at 10:37 PM.
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
A bad diode be it one or many can slowly grain the battery, call them a electrical one way check valve if bad.
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Tests for charging system-basic
Voltage test first:
Measure the voltage at the alternator output post and case with heavy electrical loads on (lights, fan, etc.) after five minutes at idle, note.
Measure the voltage right at the battery posts not the connections at the same time, note.
The difference between the two should be less than .3 volts.
The older alternators will have a output voltage around 13.8 volts, the newer alternators greater than 14 volts. The newer lower maintenance batteries of the last twenty years require the higher 14+ volts to insure there long life.
The above test will tell you more in ten minutes than anything else you can do. It is better to test first then attack the problem to prevent wasted time and parts. Once you touch anything with wiring you do not know if you fixed the problem or made it worse.
This test will tell you if the alternator is producing the correct output voltage or if the wiring is at fault for poor connections in the charging circuit. This is very quick to do and should always be the first test when having electrical charging issues with voltage problems on any system.
As mentioned in the previous post test for current drain with a test light or current meter inserted in series with the battery at the battery connection. Just remember some devices use current all the time, a clock for example.
There is a misconception that a larger alternator rating will charge more but this is not really true. The maximum output rating of an alternator is only produced at very high RPM's. Most of the time the engine is at lower RPM's and many alternators of lower rated maximum outputs will produce more power at lower RPM's. The output of a alternator is greatly reduced at the lower RPM's.
The only way to fully test the output of any alternator is to run a proper test to look for shorted windings, open or leaking diodes, bad brushes, etc. and this can only be done at a good shop. For the most part though if the voltage is proper than the system is most likely ok.<!-- / message --><!-- one sig per page -->
Measure the voltage at the alternator output post and case with heavy electrical loads on (lights, fan, etc.) after five minutes at idle, note.
Measure the voltage right at the battery posts not the connections at the same time, note.
The difference between the two should be less than .3 volts.
The older alternators will have a output voltage around 13.8 volts, the newer alternators greater than 14 volts. The newer lower maintenance batteries of the last twenty years require the higher 14+ volts to insure there long life.
The above test will tell you more in ten minutes than anything else you can do. It is better to test first then attack the problem to prevent wasted time and parts. Once you touch anything with wiring you do not know if you fixed the problem or made it worse.
This test will tell you if the alternator is producing the correct output voltage or if the wiring is at fault for poor connections in the charging circuit. This is very quick to do and should always be the first test when having electrical charging issues with voltage problems on any system.
As mentioned in the previous post test for current drain with a test light or current meter inserted in series with the battery at the battery connection. Just remember some devices use current all the time, a clock for example.
There is a misconception that a larger alternator rating will charge more but this is not really true. The maximum output rating of an alternator is only produced at very high RPM's. Most of the time the engine is at lower RPM's and many alternators of lower rated maximum outputs will produce more power at lower RPM's. The output of a alternator is greatly reduced at the lower RPM's.
The only way to fully test the output of any alternator is to run a proper test to look for shorted windings, open or leaking diodes, bad brushes, etc. and this can only be done at a good shop. For the most part though if the voltage is proper than the system is most likely ok.<!-- / message --><!-- one sig per page -->
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