Alternator not charging
02-13-2010, 03:16 PM
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Alternator not charging
Need help tring to figure out why alternator is not charging, replaced it three times still not charging,has drained the battery twice had to replace them .If I charge the battery from my ford it charges the alt.but as soon as I take it off the battery it drops back down to 8. Checked all wires nothing.
02-13-2010, 03:28 PM
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Check the fuse in the fuse box. I hit my alt changing the oil with the filter and popped it (had exposed wire). Mine did not look like it was blown till I really looked at it like the third time. Hope that's it. I couldn't find one except at the dealer. I hate electrical stuff. Good luck.
02-13-2010, 03:40 PM
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We need you to fill out your signature so we know what year your truck is. Troubleshooting is somewhat different from year to year.
The first thing you should do is isolate the batteries from each other, then charge them each completely and test them separately. You need to make sure they are good, and not confusing your test results. If they are only reading 8 volts, you may have one shorted battery or a dead cell.
The next thing you need to do is, with the key OFF and removed, (after the batteries have been re-installed) use a test light to check for power at the big charge terminal at the rear of the alternator. There should be power there. If there is not, check the big charge fuse in the Power Distribution box under the hood. It is rated at around 140 amps.
Next, there are two smaller terminals on the back of the alternator. They control the field circuit which determines the voltage output. One should have a constant 12 volts with the engine running, the other is a ground which the voltage regulator will vary in relation to the system voltage. With the truck idling and the system voltage low (below, say, 13 volts) hook your test light between the two terminals. It should light up brightly. If it does not, you need to determine if it is the 12 volts or the ground that is missing from the circuit. The 12 volts comes from the ASD relay which is turned on by the PCM when it recognises that the engine is running. The ground is controlled proportionally by the voltage regulator which is internal to the PCM.
Hope this helps. I know it looks pretty complicated, but get as far with the troubleshooting as you can, then we're here when you need us.
The first thing you should do is isolate the batteries from each other, then charge them each completely and test them separately. You need to make sure they are good, and not confusing your test results. If they are only reading 8 volts, you may have one shorted battery or a dead cell.
The next thing you need to do is, with the key OFF and removed, (after the batteries have been re-installed) use a test light to check for power at the big charge terminal at the rear of the alternator. There should be power there. If there is not, check the big charge fuse in the Power Distribution box under the hood. It is rated at around 140 amps.
Next, there are two smaller terminals on the back of the alternator. They control the field circuit which determines the voltage output. One should have a constant 12 volts with the engine running, the other is a ground which the voltage regulator will vary in relation to the system voltage. With the truck idling and the system voltage low (below, say, 13 volts) hook your test light between the two terminals. It should light up brightly. If it does not, you need to determine if it is the 12 volts or the ground that is missing from the circuit. The 12 volts comes from the ASD relay which is turned on by the PCM when it recognises that the engine is running. The ground is controlled proportionally by the voltage regulator which is internal to the PCM.
Hope this helps. I know it looks pretty complicated, but get as far with the troubleshooting as you can, then we're here when you need us.
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