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Discussion Starter #1
So recently I have been having a random strange issue. The other day while driving, Check gauges light came on and the battery meter dropped to 8. Other then this I did not seem to notice anything weird. When I turned the truck off and started it again it was working fine again. This seems to be random.

I did test at the battery while the check gauges light was on and it showed around 12.6. I would think it should show 14+. So this makes me think possibly the alternator. But I also read something about these trucks have a limp mode when they detect an electrical issue. Any help would be appreciated.
 

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Check your battery cables for stiffness. There should be a consistent flexibility throughout the entire cable. If any stiff spots are present the cable needs to be changed. Have your batteries load tested. Also make sure the connections are clean and tight. When the grid heater turns on it puts a major load on your batteries and if there’s connection/cable issues they show themselves by dropping the voltage.
 

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Was the engine running when you checked the volts? Make sure all grounds and battery connects are clean and snug
 
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These trucks are very picky about having good clean and tight 12v connections.
 
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tested at which battery
 

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then unless I'm thinking wrong, on the passenger side it's the negative to the engine block or the positive from the alternator to the battery that's not making a good connection.
 

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Discussion Starter #8
Check the connections once more. They are all tight and won't budge. Now looking at the cable from the alternator to the battery, it's pretty slim. Is it supposed to be smaller gauge then the other cables? Anyway testing at the alternator positive out, it's showing 12.4v so I'm thinking alternator.
 

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Have it tested prior to just replacing it.
ECM controls the Alt output amount
 
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What is truck info, different wiring on different years??
Any codes? ECM monitors EVR circuit.
OEM Alternator wire is 4 gauge.
 

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Discussion Starter #11
I took the truck in to the local parts store and they tested the alternator. Tested bad. did it 3 times. Took it home and pulled the alternator and went back in. Had them test the alternator, again failed 3 times. Bought a new one, (reman). Put it in, also replaced the wire from the alternator to the battery. The truck is showing 14.26v on both batteries. No issues so far except now my brake controller seems to think a trailer is connected...
 

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Good to hear of the fix. (y)

What year is your truck?
 

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Yeah if you're only getting 12.6 on each battery with the engine running, the alternator is a good place to start looking into. Glad it's fixed.
 
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