Underhood fuse box removal

[Sleeper]

Looks like it have a broken wire somewhere in the firewall bundle and I'm going to need access to the harness boot from the engine side because I can barely get a couple fingers on the harness cab side even with the bcm removed. Does anyone have a diagram of the under hood fuse block/junction box and the removal procedure they could send my way? There's gotta be a clip or bolt that I'm not seeing which isn't allowing the box to release. Also wondering if theres a second battery associated with the propower onboard that I need to worry about when disconnecting the leads off the box or if simply removing the battery is enough to safely disconnect the leads coming off the fuse block, or do I need to isolate each lead individually as I pull them off?

Truck is a 2025 f150 tremor with 3.5 and pro-power onboard. Also has anyone removed the connectors around the passenger side footwell without breaking off the tabs that hold it together? I tried pushing, pulling, squeezing, tried to force the connector together thinking it may have been a pressure clip, nothing seems to work. The harness moves but appears to be attached to the body with either one of the strongest Christmas tree plugs I've ever tried to remove or its riveted in there because I can spin it all around but can get no separation from the mounting location. Googled a picture of the type of clasp it has, seems to be a common problem with these breaking when trying to remove so id like to avoid that if possible.

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[deanfx]

Why not take it to a dealer if it’s a 2025? Just curious.

 

[Buyer2021]

Why not take it to a dealer if it’s a 2025? Just curious.

Per another forum thread the problem is caused by the OP while doing a mod (routing additional wires through firewall), therefore not covered under warranty.

Fix is likely $$$$ at dealer.

@Sleeper , just FYI, being curious I scoured the Ford Workshop Manual for my 2022 F150 and found NO information whatsoever about removal / replacement of any of the fuse / junction boxes (!).

Good Luck!

 

[Sleeper]

Fix at the dealer is likely replace entire wire harness so I'm guessing not cheap. So for now my options are to find and fix the wire which requires removing the box and connector. I could find the pin on the in cab connector and run a new wire entirely up to the radar harness, or I can live without cruise control which is really annoying mainly because of the constant pop-up everytime I turn the truck on.

My plan at this point is to make a meter lead long enough to ohm out the pins from the front radar harness to the harness in the passenger footwell and at least see what wire is damaged.

 

[deanfx]

Man if I had a 25, I’d let the dealer fix. Cost would be irrelevant. It’s just a broke wire. Can’t be that expensive.

 

[Kanuck]

It's the labor rate the dealers charge. Also, there is no set time for repair, so the tech can milk it if he so desire. As an electrician, these were EXTRAS and were time and material..... like getting a bonus.

 

[Sleeper]

Man if I had a 25, I’d let the dealer fix. Cost would be irrelevant. It’s just a broke wire. Can’t be that expensive.

I came from owning Dodges so every fix defaulted to "replace everything" with the problem most likely being my fault I'm guessing at minimum its a complete replacement of wiring harness which means dash removal and likely several thousands to repair. Its not effecting drivability and I'm reasonably experienced with electrical it would be a quick fix if I had even a couple of inches to get my hands at the harness or at least actually see which wire is broken.

I got my forscan module today so gotta read up on that and I'm just going to start checking resistance on each side of firewall till I find which wire or wires have no continuity. I have like 2 ford dealers within 50 miles of me and cant say id trust either one, even when I bought the truck they tried changing the purchase terms overnight after deposit was made so I know I won't take it to that dealer. If my continuity experiment doesn't work I may have to just bite the bullet though.

My main concern after this though is how ford is with warranty and modifications? I mean the truck has upfitter switches as a feature, they have to know people would be modifying things.

 

[deanfx]

I came from owning Dodges so every fix defaulted to "replace everything" with the problem most likely being my fault I'm guessing at minimum its a complete replacement of wiring harness which means dash removal and likely several thousands to repair. Its not effecting drivability and I'm reasonably experienced with electrical it would be a quick fix if I had even a couple of inches to get my hands at the harness or at least actually see which wire is broken.

I got my forscan module today so gotta read up on that and I'm just going to start checking resistance on each side of firewall till I find which wire or wires have no continuity. I have like 2 ford dealers within 50 miles of me and cant say id trust either one, even when I bought the truck they tried changing the purchase terms overnight after deposit was made so I know I won't take it to that dealer. If my continuity experiment doesn't work I may have to just bite the bullet though.

My main concern after this though is how ford is with warranty and modifications? I mean the truck has upfitter switches as a feature, they have to know people would be modifying things.

Man I hate to hear that about your dealers. My dealer would prob fix the issue for me. But I am a repeat purchaser as well. And respect to you for trying to sort the issue for sure. If you don’t mind me asking, what were you trying to do to create the issue? I also came from the Cummins world, and was always changing something on those trucks. And those dealers were way worse than my ford dealers.

 

[Sleeper]

I ran a power wire for an amp and a couple aux wires to the rear for amp turn on and an eventual rear light setup i want to do but I got those wires from the kick panel. So only the power wire went through the grommet I saw a ton of people recommending, the little nipple above the main wire harness. I used fish tape to get through from engine side taped everything up nice and smooth to avoid catching and used some soap to pull through the 4g wire with a little resistance at first then it just pulled through fine.

At first I thought maybe the amp was messing with some voltage signal I wasn't aware of or possibly a bad Ground so I regrounded another spot, added an extra 18" ground from battery to chassis just to make sure everything ground wise was in a good spot but the warning never went away. Stuck an endoscope up to check wire harness and the wire came in tight but appeared to be above the main bundle so it must have damaged it inside the harness boot.

Another member here ran the vin and found a code for lost communication with cruise control module and forward sensing module. If i can get into the boot and find no internal damage I'll take it to the dealer, but if I took it to them now they are just going to say the modification did it. Which is probably the same thing id do in their situation to be honest, I don't have the greatest experiences at brand dealers in my area, they all know they are really your only option and definitely use it to their advanatge.

 

[kd-]

Wondering if anyone else figured this out - I have the service manual steps for 2021 below (assuming it's the same for later years) but I have no idea how to get the clips released, they are really far back there. I can get it half-loosened but that's about it.

I found on an F250 video that these bolts hold in the connectors on the bottom, and they seemed to get totally removed, but... for the life of me I can't get these 4 tabs released, especially the ones towards the firewall

(for completeness)

 

[kd-]

Oh, and a picture from the top - red I'm pretty sure are tabs that need to be released and were easy to do so, yellow are the ones I think are tabs but are hard to release (or maybe they're just retaining clips for the lid and I'm looking in the wrong place)

Where the green arrows are, there are mounting brackets bolted to the body that hold everything in place, but I don't think those should have to be removed...

If relevant, my real goal is to remove the Battery Junction Box on the right to replace a 125A fuse, and my impression is the whole BCMC unit has got to come out to make that happen.

 

[Porpoise Hork]

 

[Tired Lizard]

If relevant, my real goal is to remove the Battery Junction Box on the right to replace a 125A fuse, and my impression is the whole BCMC unit has got to come out to make that happen.

My guess is remove the corner nut, then one fuse strip lays on the the other and clips hold them on.
Maybe like an older one: BJB fuse box and mega fuses!

Bottom:

 

[kd-]

My guess is remove the corner nut, then one fuse strip lays on the the other and clips hold them on.
Maybe like an older one: BJB fuse box and mega fuses!

Bottom:

Thanks for the video link, that was helpful, and the ticket!

The BCMC does not have to come out to remove these high-amperage battery junction box fuses. It's as easy as:

1. Removing all the wires coming into the BJB and setting aside
2. Sticking a pry bar between the outer part of the BJB and the fuse assembly, then pulling up on the fuses once those clips are disengaged.
   1. One on top of the other like you said. Closest to the right red arrow in my picture, but a little further in
3. Pulling up on the fuse assembly - the protruding bolts are a reasonable place to put some pliers on and pull. I pulled on the plastic and accident broke part of it, but you could do that too carefully.

I was breaking (other) plastic trying to pry in other spots and now it seems really obvious. Hopefully I never have to remove that thing for another reason!

 

[GSteirer]

The BCMC does not have to come out to remove these high-amperage battery junction box fuses. It's as easy as:

1. Removing all the wires coming into the BJB and setting aside
2. Sticking a pry bar between the outer part of the BJB and the fuse assembly, then pulling up on the fuses once those clips are disengaged.
   1. One on top of the other like you said. Closest to the right red arrow in my picture, but a little further in
3. Pulling up on the fuse assembly - the protruding bolts are a reasonable place to put some pliers on and pull. I pulled on the plastic and accident broke part of it, but you could do that too carefully.

I was breaking (other) plastic trying to pry in other spots and now it seems really obvious. Hopefully I never have to remove that thing for another reason!
[/QUOTE]


Were you able to locate a broken wire, and find what was wrong? I just did the same exact thing, but my tailgate actuator went out instead. I also ended up using the lower grommet when I couldn’t get a fish stick through the upper one also. I have an appt at the dealership, but it isn’t until Jan 26, 26 and my warranty will likely be up by then.

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