Battery light
Intermitent Battery Light
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Junior User
Joined: Dec 2007
Posts: 53
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From: West Michigan
Intermitent Battery Light
I have my tuner set to show Battery Voltage. I had a battery light come on, NO DTC's Thrown, Took Alternator out and had checked, Tested at 15 Volts. Belt checked good, Batteries ?, so installed 2 new NAPA Bat's, Battery light is still an intermittent Problem. When Bat light comes on Bat Voltage drops to between 11.7-12.2 when Bat light goes out Bat. Volt reads from 13.2-14.0 . Some times seems to be rpm related, but other times means nothing. At times I hear a high pitch sound, (other than Turbo). I get home jump out and put volt meter across battery and get between 12.2-12.5 . I am not made of money and can not afford to throw money at this thing. Any help would be appreciated. Thanxs
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Joined: Nov 2008
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If the alternator test is valid, the only other cause is likely a bad connection. Check all your cables and ground straps for corrosion. Some vehicles can have a problem where the positive cables are connected together (pairing diesel batteries). Etching over time will degrade the connection and can cause large intermittent voltage swings. The big draw from cranking temporarily welds the connection point together and it seems OK for a while. When it gets bad enough the engine will stop for an instant then catch again.
These events don't normally make the alternator light come on, they just cause voltage swings. A flaky alternator light is usually from a bad diode.
These events don't normally make the alternator light come on, they just cause voltage swings. A flaky alternator light is usually from a bad diode.
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Junior User
Joined: Dec 2007
Posts: 53
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From: West Michigan
If the alternator test is valid, the only other cause is likely a bad connection. Check all your cables and ground straps for corrosion. Some vehicles can have a problem where the positive cables are connected together (pairing diesel batteries). Etching over time will degrade the connection and can cause large intermittent voltage swings. The big draw from cranking temporarily welds the connection point together and it seems OK for a while. When it gets bad enough the engine will stop for an instant then catch again.
These events don't normally make the alternator light come on, they just cause voltage swings. A flaky alternator light is usually from a bad diode.
These events don't normally make the alternator light come on, they just cause voltage swings. A flaky alternator light is usually from a bad diode.
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From: round rock, tx
the 99 had the older LEAD version battery cables. They can be old and wornout. Check all connections. Consider upgrading to the newer 01 style SS connectors. The batt post connector on the passenger side gets loose and doesn't tighten again very well, plus it holds the + wires for both batterys
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Joined: Sep 2006
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This is what I had on my 99 F250 SD 5.7L . Check in line fuse link from alt to starter solenoid ,it is just before the solenoid. Mine had corrsion problem under heat shrink seal.
This looked good from the outside untill I removed seal to find problem.
This was done 4 days ago on my truck.
good luck.
This looked good from the outside untill I removed seal to find problem.
This was done 4 days ago on my truck.
good luck.
