Keeps blowing 20-amp alternator fuse

Tiny
GENEKYNISTON
  • MEMBER
  • 2001 LINCOLN NAVIGATOR
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 300,000 MILES
Every time I put a new 20-amp fuse for my alternator in my box it blows.
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Friday, March 25th, 2022 AT 12:14 PM

3 Replies

Tiny
AL514
  • EXPERT
Hello, which fuse exactly do you have to keep changing? Looks like Fuse #11. The only component on that circuit seems to be the Alternator. So, either that wire has a break in the insolation somewhere or the Alternator itself has a short to ground internally. So, you can trace that wire back to the Battery Junction box where the fuse is, it's the orange/light blue wire coming from the Alternator.
You can also try unplugging the Alternator connector that has that orange/light blue wire and turn the key to the "on" position and see if the fuse still goes. If it doesn't then most likely the problem is internal to the Alternator.
Do you own a basic multimeter? If you find that the fuse still goes with the Alternator unplugged. You can check for continuity from the Alternator connector to ground with the fuse out. That will tell you if the wire is touching ground somewhere. After years of engine vibrations sometimes the wiring harness will rub through contact points. This vehicle being a 2001, it can definitely be an issue. But try unplugging the Alternator first, don't start the vehicle, just turn the key on. We would usually put an automotive fuse breaker in there to prevent having to replace the fuse while trying to find the short circuit, but those kits are pretty expensive. Let us know what you find.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

https://www.2carpros.com/articles/how-to-check-a-car-alternator

https://www.2carpros.com/articles/how-to-use-a-voltmeter
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Friday, March 25th, 2022 AT 1:41 PM
Tiny
GENEKYNISTON
  • MEMBER
Yes, it is a short in the wire. How do I replace it without tearing out all the wiring harness?
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Friday, March 25th, 2022 AT 3:29 PM
Tiny
AL514
  • EXPERT
Well, honestly its best to find where the short in the harness is, because if it is a place where the harness has rubbed through on a contact point, there is most definitely going to be other wires there that, if they're not effected already, they will be shortly. And because the wire you're tracing down is running from the engine compartment junction box to the Alternator, the short is in the engine compartment. You don't have to go taking half the car apart to find a short somewhere in the middle of the dashboard. Thats when it becomes a real issue.
I would start at the Alternator and just move along the harness, not moving it much, you don't want to move the short away from its bad spot, you may never find it then. But go along and stop at the first spot where the harness is contacting the engine block, or a harness fastener. Any spot that could potentially have rubbed through. Just keep in mind heat and vibrations and contact points. Thats where short circuits will be.
Another option if you have a multimeter. It is to set the meter on the ohms setting, unplug the alternator and put one lead of the meter clipped to that orange/light blue wire and the other end, pull the blown fuse, and you should read continuity on that wire to the fuse from the Alternator. Since this isn't an open circuit, you can watch the meter and do a wiggle test of the harness and watch the meter. When you come to the short you should see the ohms reading on the meter change, that means you're close to the short.
You will have to open the harness, but right now you're only dealing with one wire. Once you find the short, inspect the other wires around it for damage as well. You might find something you weren't expecting at all. But the situation could be much worse.
I believe the Alternator is right on top on this model.
I added 2 OEM diagrams below, there is a connector the wire runs through. 169M, its location is in the 2nd diagram. To help you get an idea of what path that wire takes to the Junction Box.
You don't need to take out the whole harness, you just need to follow that wire.
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Friday, March 25th, 2022 AT 4:48 PM

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