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EricFromCT
EricFromCT, Ford Technician
Category: Ford
Satisfied Customers: 4022
Experience:  20 years dealership exp., ASE A1-A9 L1 L2, Ford Lincoln Mercury Senior Master, Diesel Certified
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2013 Ford F-350 6.7 L diesel. Battery light comes on approx

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Hello. 2013 Ford F-350 6.7 L diesel. Battery light comes on approx 10 seconds after starting truck and stays lit. New alternator installed, checked 2 of 3 wires to alt plug ok. Looking to check the red wire that runs from the alt to the pcm. Am I on the right track? Or looking in the wrong area?

Hi. Welcome to chat! My name is ***** ***** I am currently a factory dealer auto mechanic. I will attempt to assist you with your concern today.

You are on the right track. I have seen that red wire chaff in the harness that runs down the engine along under the water pump.

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Customer: replied 28 days ago.
Hello. Thank you

You are on the right track. I have seen that red wire chaff in the harness that runs down the engine along under the water pump.

Please note that customer satisfaction is my number one goal. Also we can respond in this chat back and forth many times. I may be offline when you respond but I will promptly reply when I return.

Thank you for rating my assistance and for using Just Answer.

Customer: replied 28 days ago.
I was having trouble locating the red wire. What is the best way to access it? Is it common to cause this exact issue?

I have seen this on 2 other vehicles with a 6.7 One I found by accident when replacing the water pump and the wire was easy to get to. I think without all the removed your best bet is to go underneath and you will see the harness bolted to the bottom of the engine. A lot of people will just run a test wire from the alternator to the pcm to see if the charging light goes out. To bypass the circuit in question. Then if it works they just overlay their own wire to complete the repair instead of digging around in the harness in a hard to reach location.

Please note that customer satisfaction is my number one goal. Also we can respond in this chat back and forth many times. I may be offline when you respond but I will promptly reply when I return.

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Customer: replied 28 days ago.
I understand. I noticed there is a fusible link on that same red wire, I would definitely like to bypass the wire rather than dig in the harness as you pointed out. Will bypassing the fusible link be ok? Also, which connector does the red alt wire go to? I'm having trouble locating it, I have alldata DIY, but I can't seem to figure out it's actual location under the hood.
Customer: replied 28 days ago.
I was able to locate the other two wires from the 3 wire alt plug to a plug next to the pcm behind the passenger side battery, but cannot locate the red wire.

THe red wire goes from the battery junction box through the fuse link to the generator. That is the generator power. That is not the wire I have seen broken I have seen one of the others that go the pcm broken. EIther the yellow or the violet. Did you ohm out the other 2 that

go from the alternator to the pcm?

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Customer: replied 28 days ago.
I ohmed the yellow and violet wires from the alt to the pcm and they were good. I was next looking to check the small 18 gauge red wire but couldn't find where it went to.

I think the electrical diagram for the charging system may help you.

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Customer: replied 28 days ago.
I checked the yellow and violet wires only from the connector near the pcm to the 3 wire alt plug and they were good.
Customer: replied 28 days ago.
I have the wire diagram from all data. What do you think could be causing the light? Are there any other checks I can do?

Ok. Make sure the red wire has full battery voltage at the plug on the alternator. If that fuse link is weak or high resistance in the circuit the alternator will not be getting battery voltage to run.

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Customer: replied 28 days ago.
Ok I can definitely do that. The alternator is charging at 14.4. Volts as it was prior to replacement. Do you think it's possible that a weak fuse link/higher resistance would still allow the alt to operate normal? Also, where is that fuse link commonly found under the hood? Do you have any guidance on where to look for it without having to take the entire harness apart?

If the alternator is charging at 14.4 I would think that the red wire is good. If one of the monitor circuits going to the pcm was not good then the pcm would put the light because it wouldnt be able to control charging. You could try overlaying the 2 wires, just for testing, from the alternator to the pcm. Also there should be a code stored in the pcm. That may be worth checking. The fuse link is located in the front of the high current battery box which is located on the passenger side front of the engine compartment. Where the 275 amp fuse is.

Please note that customer satisfaction is my number one goal. Also we can respond in this chat back and forth many times. I may be offline when you respond but I will promptly reply when I return.

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EricFromCT and 4 other Ford Specialists are ready to help you
Customer: replied 28 days ago.
Ok sounds good. This one has been a tough diag for me. That's why I enlisted your services. I am going to try checking a few more things. Thank you for your help.

Your welcome. I understand. This stuff can be tough even for a dealer tech like myself. CHeck those things out and feel free to come back to this chat if you have further questions on this. Thanks.

Customer: replied 28 days ago.
Ok, I'll check those things and write back with further findings and let you know. Thanks again.

Alright. Thanks.

Customer: replied 26 days ago.
Hello. Eric.
I wanted to get back to you regarding the issue with the Ford F-350 6.7 diesel with a battery light. I found the problem. I unplugged the 3 pin plug at the alternator and checked for battery voltage on the red 18 gauge wire, it measured 9.0 volts with the truck off. I then stripped the wire back behind the plug while the plug was plugged into the alternator and measure voltage with the truck running and it measured 5.0 volts. I then applied battery voltage to the red 18 gauge wire while the truck was running and plugged in and the battery light went out. I now have to find where or why there is some sort of resistance somewhere in the 18 gauge red wire to the alternator. I suspect something with the fusible link or a corroded wire. Just want led to give an update, thanks again for your help.

I would say thats great but you still have to fix it. You are on the right track now for sure. I would also suspect the link or a corroded wire. Good find.