Resource: Tables showing when which fuses are HOT (Always Hot; Hot in Start or Run; etc)

[Buyer2021]

Maybe of interest, I see many posts where folks ask what fuses are hot for various purposes. I compiled this from the Ford Service Manual for 2021-2022 F150, the wiring diagrams showing Power Distribution.

One PDF for the Body Control Module (fuse box in the cabin)
One PDF for the Battery Junction Box (fuse box in the engine compartment)
3 Categories of function are listed

• Hot in Start or Run
• Hot at All Times
• Relay Control

"Relay Control" means the fuse is Hot when certain vehicle systems are activated; the relay is controlled by a vehicle module such as the PCM, etc. That's where you may find fuses that go Hot with ACC On without Start / Run; some of those may be subject to delay shut-off after engine off; some of the Relay Control fuses may be subject to 'going cold' even when the 'key is on' as managed by the Battery Protection System (to prevent killing the starter battery). You'll have to test to figure out the behavior of those, it's too complex and varied for me to tabulate.

• ALWAYS VERIFY FUSE FUNCTION BEFORE USING
• The lists may not be complete and not all trucks may have all fuses listed
• Not all fuses listed are 'blade-type' that lend to fuse taps
• If you install a tap be sure to test to find the 'Hot Leg' and orient your tap properly!

Hope this is helpful, Have Fun!

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[Grafx36510]

And this is what forums are meant for! Thanks for this.

 

[air2mag]

Thanks for putting this together!

 

[Kanuck]

Great info....thanks

 

[mrtull]

Maybe of interest, I see many posts where folks ask what fuses are hot for various purposes. I compiled this from the Ford Service Manual for 2021-2022 F150, the wiring diagrams showing Power Distribution.

One PDF for the Body Control Module (fuse box in the cabin)
One PDF for the Battery Junction Box (fuse box in the engine compartment)
3 Categories of function are listed

• Hot in Start or Run
• Hot at All Times
• Relay Control

"Relay Control" means the fuse is Hot when certain vehicle systems are activated; the relay is controlled by a vehicle module such as the PCM, etc. You'll have to test to figure out the behavior of those, it's too complex and varied for me to tabulate. That's where you may find fuses that go Hot with ACC On without Start / Run, and some of those may be subject to delay shut-off after engine off. Some of the Relay Control fuses may be subject to 'going cold' even when the 'key is on' as managed by the Battery Protection System (to prevent killing the starter battery).

• ALWAYS VERIFY FUSE FUNCTION BEFORE USING
• The lists may not be complete and not all trucks may have all fuses listed
• Not all fuses listed are 'blade-type' that lend to fuse taps
• If you install a tap be sure to test to find the 'Hot Leg' and orient your tap properly!

Hope this is helpful, Have Fun!

Both a great reference and educational! Glass is definitely raised!!

 

[JScaro]

Can you check my VIN 1FTEW XYZ

Sorry couldn't resist.


Thanks @Buyer2021 Great job as always!

 

[Big Dog Daddy]

On the subject of Fuse's, I just recently learned that many of the BCM fuses are three bladed micro type. in different amperages. I picked up some spares on Amazon.

 

[Big Dog Daddy]

Thanks for posting a great resource!
@Buyer2021

 

[scuba]

Thanks again, and a fuse question:
For a fuse "not used" that has a 5amp fuse already present in it, should I interpret that as indication that I shouldn't exceed a 5-amp fuse if I use a fuse tap to tap into it?

(I tapped into #22, and ran wire to the console / under passenger set to power a few different things (cell booster, headrest dvd player, Roku). I don't think I'll exceed 5amps, even with that, but would like to know the answer in-general.

Thanks if anyone knows that.

 

[Buyer2021]

Thanks again, and a fuse question:
For a fuse "not used" that has a 5amp fuse already present in it, should I interpret that as indication that I shouldn't exceed a 5-amp fuse if I use a fuse tap to tap into it?

(I tapped into #22, and ran wire to the console / under passenger set to power a few different things (cell booster, headrest dvd player, Roku). I don't think I'll exceed 5amps, even with that, but would like to know the answer in-general.

I'm gonna bore you with a long explanation .....

First, let's look at the source of the info in my table for Fuse 22:

Note in the above:

• The 'bus' in the fuse box (the 'hot leg' power source) is shown as "Hot in Start or Run"
• It shows a 5A fuse for F22 but on the output let there's nothing shown connected, just the note "Not used"

So, just FYI, ^that's^ the source for my table data for F22 (and F36, F37); I went through the entire bunch of those 'cells / images' for each set of fuses in the Service Manual Power Distribution Diagrams to compile the entire table.
___________

With that explanation of my data source, I'll offer these opinions

• The "busses" within the fuse box have amp-capacity ("ampacity") to power most any likely added load one would want to impose that's within the capacity range of reputable fuse taps
• Personally I would only use reputable branded fuse taps in my F150, and those will always state the maximum ampacity of the tap device itself (see this product sheet for Bussman taps, all which are limited to 10A for the added circuit, as are taps by Littlefuse; Lumision offers a micro-3 tap claiming an ampacity of 20A per slot)
• If I ever need to add / switch more than the tap rated load, I'd use the tap as a switching source for a properly sized relay with the load side of the relay powered through a direct-to-battery connection
• Can you find other / off-brand fuse taps claiming more than 10A~20A capacity for the added circuit? Maybe, caveat emptor.
• Personally, I'd always insert the same fuse as found OE in the lower-slot of the tap even thought the WSM says it is "Not used"

So, in summary of my opinion , you're OK tapping any fuse in the box with any added circuit amperage within the limits of the tapping device itself.

Hope that helps, Have Fun!

 

[fluffernutter]

Not sure if this is helpful as well:
https://www.startmycar.com/us/ford/f-150/info/fusebox/2021#anchorfusebox0

I used this when putting in the under hood LED light strip.

 

[cghall77]

Excellent, thank you for this. Just about to search when I saw this was unread. Hoping to install 12v and usb adapter in bed with 2kw. Don't want to go direct from battery in order to have some level of battery protect. Hoping to find something that is available for 30-60 minutes after engine shut off.

 

[HeadBanger]

On the subject of Fuse's, I just recently learned that many of the BCM fuses are three bladed micro type. in different amperages. I picked up some spares on Amazon.

I did the same thing.. Picked up the wrong 'add a fuse' kit.

 

[HeadBanger]

OP, thanks for posting this up! Good stuff!

 

[Gutshot]

Yes, thank you OP, handy info indeed

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