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1209 Views 9 Replies 5 Participants Last post by  rogainer, 
rogainer
So my truck is getting hard to start because of low voltage. I though it was batteries but i checked them with a volt meter with the truck off and they read 12 volts. When im driving my dash volt meter reads 8 and jumps up to 14 (i know its grid heater.) But also when im driving my lights go dim and radio shuts off and comes back on constantly. My check gages light came on and i dont have any codes. I just want to make sure this is alternator before i take it off and replace it. :confused013:
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W
need to load test your batteries with a real load tester. same machine can be set up with the amp clamp on the charge cable and will show if it's charging
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rogainer
Alright ill give it a shot, thanks!
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B
Above is correct, you need load test. It is cranking amps that counts, not voltage. Then buy the biggest highest amp batteries you can get in there.
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rogainer
Ended up being the alternator, got one from o'reillys and the gave me one with a bad bearing so now I have to get another one


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D
Did you check each battery individually? They should use a carbon tester set at 1/2 the CCA for 15 seconds and quickly read the voltage, temp compensate it. That requires a fully charged battery so you may need to use an AC charger.

Wait a few (5) minutes between testing of each battery as the tester is pulling a lot of current and needs to cool down. Its OK if it smells a bit hot.

The places that test batteries probably use a conductive battery tester which is OK, but a load test is better.

No way your grid heater will pull the actual battery voltage down much. They may drop the voltage that the alternator is putting out down to battery voltage.
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Mopar1973Man
Starter draw is typically 400-700 Amps

Grid Heaters are 95 Amps a piece For both grid heaters 190 Amps.

I would load test both batteries and if one fails replace both batteries.
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rogainer
The load test checked out good. Took the new alternator back and got a new one and that fixed the problem. They sold me one with a bad bearing the first time. Thanks for all the info!! Now just have to figure out why my left light only has 8 volts!


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Mopar1973Man
rogainer said:
The load test checked out good. Took the new alternator back and got a new one and that fixed the problem. They sold me one with a bad bearing the first time. Thanks for all the info!! Now just have to figure out why my left light only has 8 volts!


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Check the fuse?
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rogainer
I've changed it but they were all used but not blown, checked all grounds and replaced multiswich as well.


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