What is this?
What is this bundle of cut wires? They're under the hood right in front of the firewall on the driver's side.

 

Upfitters? Thats where they are on my 19. My 12 had them under the dash, but seems Ford just puts them either or depending on year.

 

Ignorant here, what's an upfitter?

 

They’re extra wires that ford runs through the firewall because they understand that people are going to add stuff to trucks.

Some trucks even already have switches in the cab that don’t do anything factory, these switches are called unfitter switches as they’re just there for the customer to attach accessories to.
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Ford puts those blunt cut wires in both places, under the hood and under the dash, every year.

Those are called pass through circuits, because they pass through the fire wall, and that is why they are available under the dash and under hood every year, otherwise, what would be the point of providing the pass through circuits? Each wire is one and the same wire, where one end of it emerges under the hood, and the opposite end of it emerges under the dash.

The pass through circuits are provided even without the Upfitter's switch package. Even earlier trucks built prior to Ford introducing Upfitters still had those pass through circuits, because that is all those wires do... pass through the firewall, so that one does not have to drill a hole in a grommet and create a leak issue or nick a factory wire, nor drill a hole through the firewall sheetmetal and create a corrosion issue, in order to run a wire from the engine compartment to the cab.

One can certainly use these wires in coordination with Upfitter's switches, but one doesn't have to. There is no connection between these pass through wires and any fuses, relays, switch panels, or network module in the vehicle. The wires are simply wires that pass through.

There are typically four of them. Red, OffWhite, Black, and Bluish Green. None have stripes. It is easy to confuse them as trailer brake control wires, which have a similar color scheme among industry standard aftermarket trailer brake controllers.

Ford usually shrink wraps the ends of these wires, where all of them look like they have flat black rubberized tips a little over an inch long. Since there are no shrink wrapped tips visible on the wires shown in the image of Post #1, it appears that someone has either utilized or tested those wires before, because the shrink wrapped tips are cut off.

 

Excellent write up, thank you.

 

My 2007 F-250 pass-through were not heat shrink wrapped.

 

OK, those were not on my 2012, which only had 4 upfitter switches. Looks like they were added when Ford went to the 6 upfitter switches. I did find them on my 2019 where the PO wired in a compressor in the bed, but no spare wires on either side on the 12.

 

Those same four wires are on my 2000, with zero upfitter switches. They are also on both 2002 trucks 50 yards away from me, also with zero upfitter switches.

Those pass through wires are independent of the presence or lack thereof of upfitter switches. There are no related dependencies. The pass through wires have been a fixture in all Super Duties since the beginning.

 

The pass through wiring is separate from the upfitter switch wiring. 2 totally different bundles.