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How to diagnose fuses not working in fuse box

Tiny
WAYNE MERTZ
  • MEMBER
  • 2001 FORD EXPEDITION
  • 0.5L
  • V8
  • 4WD
  • AUTOMATIC
  • 250,000 MILES
There are several fuses in the inside fuse box that do not light up when I test them, even with the ignition on. Can you direct me to where to look to solve this problem? I have tested all fuses and they are good.

Thanks,
Wayne
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Wednesday, April 1st, 2020 AT 8:27 PM

9 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good morning,

I need to know which fuses and which fuse block so I can get you a power diagram.

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

What accessories do not work in the truck?

https://www.2carpros.com/articles/how-to-check-wiring

If you can give me the complete VIN number, that will help me with the diagram.

Roy
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Thursday, April 2nd, 2020 AT 3:56 AM
Tiny
WAYNE MERTZ
  • MEMBER
  • 13 POSTS
I sent a picture of the fuse box inside the truck with the fuses that I cannot get to light up.
I was working on the rear airbags not working. No power to the height adjustment switch.
I haven't check the other items where the good fuses are not lighting my meter when I check them.
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Thursday, April 2nd, 2020 AT 6:43 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Okay, 21 is powered only in the start position of the key.

The other fuses are powered by the ignition switch.

Sounds like you have a bad ignition switch. Once you verify power to the fuse block, then it could be the fuse box itself.

The fuse block is also called the GEM module and it is a common failure for not powering the fuses as well.

https://www.2carpros.com/articles/how-to-check-wiring

If you have an advanced scan tool, you can monitor the inputs and outputs of the module to verify it is working.

Roy

Removal
1. Disconnect the battery ground cable.
2. Remove the instrument panel steering column cover.

imageOpen In New TabZoom/Print

3. Disconnect the ignition switch electrical connector.
1 Loosen the bolt.
2 Disconnect the electrical connector.

imageOpen In New TabZoom/Print

4. Remove the ignition switch.
1 Remove the screws.
2 Remove the ignition switch.

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Thursday, April 2nd, 2020 AT 7:02 AM
Tiny
WAYNE MERTZ
  • MEMBER
  • 13 POSTS
What is strange is that although I could not get the fuses to light up, I did verify that those devices powered from the fuses still work, ie; the head lights work high and low beams and the dash dimmer switch works.
Strange.
I still have to trace the wires for the height adjustment switch in the back to see why no power to the switch.
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Thursday, April 2nd, 2020 AT 6:58 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, keep me updated.

Roy
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Thursday, April 2nd, 2020 AT 7:00 PM
Tiny
WAYNE MERTZ
  • MEMBER
  • 13 POSTS
Well, it appears that things are running backwards in the fuse box on those fuses that I had previously mentioned. All these fuses work when the switches for them are activated. Example: The fuse for the low beams will get the required voltage when the lights are turned on. The fuse for the high beams will get power once the high beam switch is activated. Would this indicate that there is something wrong with the ignition switch?
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Friday, April 3rd, 2020 AT 10:34 AM
Tiny
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No, it indicated power is only sent to them when the components are activated. That is not an issue. That is the way it has been designed.

Roy
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Friday, April 3rd, 2020 AT 10:36 AM
Tiny
WAYNE MERTZ
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  • 13 POSTS
Okay, thanks.
It just seems like if there was a problem in the wires (power), the switching mechanism would burn out before the fuse!
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Friday, April 3rd, 2020 AT 11:03 AM
Tiny
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  • 52,797 POSTS
That is correct but the switches have built in circuit breakers inside the switches.

Roy
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Friday, April 3rd, 2020 AT 11:08 AM

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