 Charging Issue?, I'm terrible at solving electrical problems |
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| sdoolin |
 Apr 25 2026, 11:05 AM
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#1
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Member  Group: Members Posts: 421 Joined: 1-May 14 From: LouKY Member No.: 17,299 Region Association: None  |
Voltmeter shows between 10V - 12V at idle (and everywhere else). Voltmeter drops to 10V when headlights, flashers, and wipers switched on. Multimeter across the battery terminals at idle reads 12.5V.
Alternator was verified good several years back when I built this engine. I'm not sure what to check next? |
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| mgphoto |
Apr 25 2026, 11:30 AM
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#2
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"If there is a mistake it will find me" Group: Members Posts: 1,447 Joined: 1-April 09 From: Los Angeles, CA Member No.: 10,225 Region Association: Southern California |
QUOTE(sdoolin @ Apr 25 2026, 09:05 AM)  Voltmeter shows between 10V - 12V at idle (and everywhere else). Voltmeter drops to 10V when headlights, flashers, and wipers switched on. Multimeter across the battery terminals at idle reads 12.5V. Alternator was verified good several years back when I built this engine. I'm not sure what to check next? Isolate the battery and check voltage. If you charge the battery till it is full, see how long it takes for the voltage to drop without a load, that will tell you the condition of the battery. |
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| sdoolin |
Apr 25 2026, 11:56 AM
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#3
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Member Group: Members Posts: 421 Joined: 1-May 14 From: LouKY Member No.: 17,299 Region Association: None |
OK, so I checked some more things, and I am NOT GOOD with a multimeter. But, here's what I found (all measurements at idle):
Battery = 12.5V Green Wire from alternator and chassis ground = 4.5V Brown wire from alternator and chassis ground = 0.05V (essentially 0) Red wire from alternator and chassis ground = 13.8V |
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| mgphoto |
Apr 25 2026, 02:58 PM
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#4
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"If there is a mistake it will find me" Group: Members Posts: 1,447 Joined: 1-April 09 From: Los Angeles, CA Member No.: 10,225 Region Association: Southern California |
13.8 your alternator looks to be ok but your battery might be dead, look up minimum voltage and full charge for the battery you are using. This measurement is made with the engine off.
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| fixer34 |
Apr 25 2026, 03:35 PM
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#5
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Senior Member Group: Members Posts: 1,423 Joined: 16-September 14 From: Chicago area Member No.: 17,908 Region Association: Upper MidWest 
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QUOTE(sdoolin @ Apr 25 2026, 12:56 PM) OK, so I checked some more things, and I am NOT GOOD with a multimeter. But, here's what I found (all measurements at idle): Battery = 12.5V Green Wire from alternator and chassis ground = 4.5V Brown wire from alternator and chassis ground = 0.05V (essentially 0) Red wire from alternator and chassis ground = 13.8V Assume red wire to chassis ground reading is being made at the battery positive terminal while the engine is running? Do the same measurement across the actual battery terminals. Voltage reading should be the same, or very close. If it isn't, check/clean the battery terminal connections, the red wire connection to the positive post, the ground strap from battery to chassis, and the chassis strap underneath to the transmission. Unbolt and make sure the connections are clean/shiny. |
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| sdoolin |
Apr 25 2026, 04:13 PM
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#6
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Member Group: Members Posts: 421 Joined: 1-May 14 From: LouKY Member No.: 17,299 Region Association: None |
Battery is virtually new, and lives on a trickle charger when not being driven. Terminals clean and tidy. All grounds clean and tidy and nice and tight.
Red wire measurement is between the wire/terminal and the chassis ground that lives next to the relay board. |
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