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Strange electrical problem!

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Old Jul 22, 2023 | 10:19 AM
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Default Strange electrical problem!

Hi everyone, new to this forum and hoping someone can help me out here.

I’m working on a 78 Anniversary with an electrical problem.
The gen light was staying on and someone installed a wrong alternator
The voltmeter was marking below 8 volts.
So, changed the alternator with a 80 amp unit.
all cables are attached and ok.
The gen light is stil on and the voltmeter still shows below 8 volts.
The output of the alternator is close to 14 volts, so ok. Battery is new and gives 12.30 volts.
I opened the Center dash to check there. Tested the voltmeter with a separate battery and works perfect. When I measure at the voltmeter I get about 5 volts, even with running engine.
This is a mystery to me!!

Anyone any idea?
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Old Jul 22, 2023 | 10:45 AM
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Did you check for a broken contact at the double plug on side of alternator?
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Old Jul 22, 2023 | 02:09 PM
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Yes I did👍🏻
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Old Jul 22, 2023 | 02:53 PM
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Probably the ground on the voltmeter if the gauges fuse shows over 12v.


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Old Jul 22, 2023 | 03:14 PM
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I added a groundwire straight from the battery.
Also the voltgauge works perfect out of the car with a separate battery.
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Old Jul 26, 2023 | 10:33 PM
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Originally Posted by taz8000
I added a groundwire straight from the battery.
Also the voltgauge works perfect out of the car with a separate battery.
Did you by any chance change the generator light in the center cluster to LED? Cuz I believe that one has to stay old style 194 bulb.
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Old Jul 27, 2023 | 01:04 AM
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No, no bulbs were changed.
this problem suddenly appeared.
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Old Jul 27, 2023 | 02:02 PM
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Originally Posted by taz8000
No, no bulbs were changed.
this problem suddenly appeared.
Then it seems there is some electrical break between alternator to Battery. Check to see if the battery is getting fed the 14 Volts from alternator. There should be some kind of bridge next to battery. Possibly either broken wire or lose connection.
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Old Jul 27, 2023 | 02:06 PM
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Hi again,

tested that too and the battery is getting 14v from the alternator.
I’m know cars very well, but this one is a mistery to me even after I did all the tests.
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Old Jul 27, 2023 | 05:24 PM
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check harness that runs from alt, along drv fender to fuse box.
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Old Jul 27, 2023 | 06:18 PM
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Could be an issue with the plug at the back of the center gauge bezel as it plugs into the printed circuit. Sounds as if you are charging but volt meter not registering it.
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Old Jul 29, 2023 | 11:10 AM
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Have you checked what voltage you are getting both sides of the gauges fuse. If you have some corrosion there and are dropping voltage across the fuse then that would explain the low reading on the voltmeter and the charging light remaining on.
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Old Jul 29, 2023 | 11:57 AM
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Solved the problem.
The Center dash was not getting the 12 volt after the switch. New wire and works perfect,
Damn electrics!!!!
Thnx everyone for your input.👍🏻👍🏻
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