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Edward, ASE Certified Technician
Category: Ford
Satisfied Customers: 2746
Experience:  ASE certified. Auto Transmission rebuilder for Ford Motor Co. from 91 to 2000
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I was listening to the radio with the motor not running for

Customer Question

I was listening to the radio with the motor not running for about 20 minutes. I had to use my 2005 F-150 Supercrew, by then it was dark. After driving for a while the battery sign came on and the warning "check charging system" I was able to get back home. I thought the battery was low but I had replaced not long time ago. I charged the battery with my home charger, but the warning continued. I disconnected the battery with the the engine running and it turned off. I think the alternator gave up, but my question is, is there a fuse that might be blown? It happened to me on my previous 99 F-150 truck, I took it to the dealer and they said it was a fuse. I would like to know which fuse that might be, is not mentioned on the manual
JA: There are so many things that can cause battery issues. Some simple, some complicated. The mechanics have tons of experience in that area. Will the car start?
Customer: Yes, it starts
JA: Glad to hear that. How old is the battery?
Customer: It has 5 year warranty from the dealer. about 2 years old. Car is running only on battery
JA: Anything else I can tell the Ford Mechanic before I connect you two?
Customer: I would like to know if there is a fuse blown, before replacing the alternator
JA: Got it. Let's get this figured out. I'm sending you to a secure page on JustAnswer so you can place the $5 fully refundable deposit now. While you're filling out that form, I'll tell the Ford Mechanic about your situation and connect you two. You'll be on the road in no time.
Submitted: 6 months ago.
Category: Ford
Expert:  Edward replied 6 months ago.
Hello, Eddie here and I will do all I can to help. What size engine is in your truck? 5.4? or v6? Also, do you have a volt/ohm meter or 12 volt test light by chance? Thank you.
Customer: replied 6 months ago.
5.4, I have a volt meter
Expert:  Edward replied 6 months ago.
Alright, The big BLACK/ORANGE charging wire coming out of the alternator, (large gauge wire) I want you to put your Volt meter on 10-15 ohms scale, and touch the BLACK/ORANGE wire at the alternator, and the other lead touch the positive battery cable. I basically want to make sure the fusible links between the alternator and the battery are good, you should show less than 1 ohm resistance in that connection. or check the voltage at the alternator itself, and not the battery, if you have 14-15 volts at the alternator, but only 12 at the battery, that would be the issue, Also, Does the Battery light come on in the instrument cluster with just the key ON? let us know, thank you.
Expert:  Edward replied 6 months ago.
I show one 5 amp fuse in the wiring diagram, fuse 15. it's on the central junction box, but if the battery light comes on in the cluster, I'm 99.9% sure that means this fuse is good. Here is the charging system wiring diagram.
Customer: replied 6 months ago.
There is continuity there, about 2 Ohms reading. The battery light is on only with the key on
Expert:  Edward replied 6 months ago.
Alright, and if running, your only getting 12 volts? no output from the alternator? Is that correct?
Expert:  Edward replied 6 months ago.
If you have continuity from the battery positive post, to the alternator charging post, and that 5 amp fuse is good, I would go ahead and try another alternator on it at that point. Let me know if you have any further questions. Thank you.
Customer: replied 6 months ago.
Sorry, my ohmeter batteries failed, had to buy replacement. That is correct,12 volts, and running 11.72 volts
Expert:  Edward replied 6 months ago.
OK, If you have continuity between alternator and battery, and your engine ground is good, (obviously is because it cranks) then I'd put another alternator on it. Let me know if you have any further questions. Thank you.