AMP light
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Joined: Jun 2003
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From: GrandRapids MI
AMP light
I am having a problem with my truck. The battery started to go the other day when i was driving, it did this a year ago and i replaced the alternator and battery. Well this time i checked the battery GOOD 12.43 vdc. Checked the alternator while truck was running battery has 11.56 vdc. So i say oh well needs another alt. Go get one install same thing. What else could be causing my problem. I drive a 93 f-150 4.9L 4x4. AMP light is on and truck will die after driven a few miles . Thanks for any info.
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From: Virginia
Does your truck have an external regulator or an internal regulator? If external, you can check the "f" wire and see if it has voltage on it.
You can also take a voltmeter reading from ground to the output terminal on the back of the alternator with the truck off. If you don't get 12 volts there, you may have a fuse or fusible link burnt out in the output wire from the alt to the starter relay terminal.
You can also take a voltmeter reading from ground to the output terminal on the back of the alternator with the truck off. If you don't get 12 volts there, you may have a fuse or fusible link burnt out in the output wire from the alt to the starter relay terminal.
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Junior User
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From: GrandRapids MI
I'm learning this all on the fly, not sure how to check the output terminal of the ALT. Would that be the high voltage harness with three wires? The other harness is the voltage reg correct? I checked all fuses, but am having trouble finding a fuseable link where might i find this?
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From: Virginia
If you have an internal regulator, then your wiring should look something like the diagram below.
You can see the fusible link is called "j". The black/orange wire should be one of the thicker ones, and if you can read 12 volts on this wire where it hooks to the alternator, then the fusible link is good, since the black/orange is hooked directly to the battery + via the fusible link. I don't know exactly where this fusible link is, but if you follow the black/orange wire up from the alt, you should run into it somewhere along the way.
You can see the fusible link is called "j". The black/orange wire should be one of the thicker ones, and if you can read 12 volts on this wire where it hooks to the alternator, then the fusible link is good, since the black/orange is hooked directly to the battery + via the fusible link. I don't know exactly where this fusible link is, but if you follow the black/orange wire up from the alt, you should run into it somewhere along the way.
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