Ford Transit Auxiliary Upfitter Switches | Wiring Guide

Ford Transit Auxiliary Upfitter Switches | Wiring Guide

Ford Transit Auxiliary Upfitter Switches
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The Ford Transit can be ordered with the optional Auxiliary Upfitter Switches, which are located on the center console between the driver and passenger seat. Each Upfitter Switch can provide a 12V output to an auxiliary load, such as Air Lift Spring Kit Compressor, an exterior LED bar, etc. The switches behavior and wiring is different prior/post year 2020, and this guide will cover both.

Ford Transit 2020+ Upfitter Switches
Ford Transit Upfitter Auxiliary Switches (2020+)
Ford Transit Upfitter Auxiliary Switches (2016-2019)
Ford Transit Upfitter Auxiliary Switches (2015-2019)

1. Ford Transit 2020+


Most of the information we present below can be found in the Ford Transit Body and Equipment Mounting Manual (BEMM) available on Ford Body Builder Advisory Service website. We found some discrepancies between the BEMM and our van, these discrepancies were also found by other folks (per this post on Please note that Ford SVE Bulletin Q-325 correction to BEMM is in line with the information presented below.

1.1. Overview

AUX 120A43-PINYellow
AUX 240A6-PINBlue/Red
AUX 340A6-PINRed/Yellow
AUX 420A43-PINGreen/Brown

1.2. Behavior

The default behavior for all auxiliary switches is to be “powered at ignition only” (when key is in “run” position) in order to prevent a full discharge of the battery. Optionally, the behavior can be changed to “powered at all time” by the jumper fuse F15 relocation from position A to position B as shown below:

Per BEMM Jumper F15 is set to Position A (Powered at ignition) from factory. In our van, Jumper F15 was set to Position B (Powered at all time) from factory.

1.3. Gain Access

Here is how to gain access to the Auxiliary Fuse Panel (to relocate Jumper Fuse F15 if needed) and how to gain access the Auxiliary Switches Power Output (to wire your auxiliary loads):

1.3.1. Release the Glove Box Door

Press inward on the glove box (on both sides) to disengage the retaining tabs, then lower the door all the way. We weren’t able to make it work by hand, so we used a wrench to pry the sides:


You’ll then be able to lower the glove box door all the way down (notice the tabs in the photo below). At this point, you can also remove the cover located in the storage below the cup holder:

You can now see the Auxiliary Fuse Panel (A526) and the High Specification Vehicle Interface Connector:


1.3.2. Get proper lighting!

It’s dark in there. We got these LED lights; they’re small and you can fit them anywhere! We’re using them all the time in the van during our conversion:

These LED lights are VERY useful, we use them all the time! Buy on Amazon.

1.3.3. Free the High Specification Vehicle Interface Connector

Pull back on the connector to free it from the Auxiliary Fuse Panel’s cover. It’ll make things easier a bit later. The High Specification Vehicle Interface Connector is used to connect loads to the AUX 1 (20A) and AUX 4 (20A), but we’ll come back to this a bit later:

1.3.4. Remove the Auxiliary Fuse Panel’s Cover

Press the tab on the left side of the cover:

Press the tab on the right side of the cover:

Look what we got here. We finally made it to the Auxiliary Fuse Panel A526:

Enhanced. Here is the Jumper Fuse F15. Ours was set to “Position B” from factory:

And just above the aux fuse panel, we have the High Capacity Auxiliary Switch Output (C33-H). Pull it UP to detach and free it:

The High Capacity Auxiliary Switch Output (C33-H) will be used to connect loads to AUX 2 (40A) and AUX 3 (40A).

1.4. Wiring

Now that we gained access to the connectors, we can wire our load(s) to the Auxiliary Upfitter Switches. You will need the following wiring harnesses; both are provided with your van (we found ours in the glove box compartment):

  • 43-Pin High Specification Vehicle Interface Harness (P/N: KTHK4V14A11BB): AUX 1 and AUX4.
  • 6-Pin High Capacity Auxiliary Switch Output Harness C33-H (P/N: HK4V14A411JA): AUX 2 and AUX 3.

Can’t find your harnesses? You can buy them from your local Ford dealer (see part numbers above) or Buy on eBay.

1.4.1. AUX 1 and AUX 4 Wiring

AUX 1 and AUX 4 upfitter switches are wired via the High Specification Vehicle Interface (43-Pin Connector). First things first, the interface (in the glove box) comes from factory with a “blank” cover. Remove it:

Press the button in the middle, then flip the white thingy:

You can now remove the “blank” cover:

At this point we could simply connect the provided harness, then connect our load to AUX 1 (yellow wire) and/or AUX 4 (green/brown wire). But we would have a bunch of unused wires hanging around, that harness is quite bulky. That could work, but we’ll go for the clean install and transfer the YELLOW and GREEN/BROWN wire to the “blank” connector we removed in the previous step. This way we only have the wires we need:

Ford Transit Auxiliary Upfitter Switch AUX 1 AUX 4 Wiring

Remove the white part by pulling it away:


Use the tip of a (very) small flat screwdriver, or alternatively unfold and cut the end of a bobby pin (works great!):

Insert and press the tiny lever up to disengage the wire from the harness. Pull on the wire to remove it from the connector:

Simply insert the yellow wire and green wire into PIN-1 and PIN2 of the “blank” connector:

Reinstall the white plastic part and the connector is ready to go in the van!

And into the van it goes:

1.4.2. AUX 2 and AUX 3 Wiring

AUX 2 and AUX 3 upfitter switches are wired via the High Capacity Auxiliary Switch Output Harness (C33-H, 6-Pin Connector). First things first, the interface (in the glove box) comes from factory with a “blank” cover. Remove it:

The C33-H harness doesn’t have to be modified, we simply connected it to the van as-is:

1.4.3. Job Closeout

We won’t be connecting loads to our auxiliary upfitter switches at the moment, so we reinstalled the connectors and the auxiliary fuse panel cover back until we’re ready to wire them. See you next time!

Ford Transit 2015-2019

Each switch is ignition supplied (they only work when the key is in “run” position) and can provide a 12V/20A max output to an auxiliary load (such as an Air Lift Spring Kit Compressor, Exterior LED Bar, etc.).

To wire auxiliary loads to the switches, you will have to order the Motorcraft Upfitter Switch Wiring Pigtail C33-H (Part Number WPT-1408). It is NOT provided with the van! Without it, you don’t have access to the output of the switches:

Now, let’s get the driver seat out of the way because this is where we access the switches output. There are four screws to remove; two in the back of the seat:

and two screws in the front of the seat:

Don’t take the seat off yet! We still have to detach the electrical harness:

We’re now going to take the batteries cover off. We have the dual batteries option; your setup might be different!

Remove those two screws to free the metal plate:

Here is the C33-H connector! We will connect our WPT-1408 pigtail to it.

While we’re here, if you ever blow one of the Upfitter Auxiliary Switch 20A fuse, this is where to replace it (see Fuse Panel in the picture above).

The WPT-1408 Wiring Pigtail kit comes with four crimp splices and shrink tubes, but we decided to install female quick-release terminal instead. This way, we can easily add or change the loads in the future:

We can now connect the WPT-1408 Wiring Pigtail Kit into the C33-H connector:

Now turn the ignition on and flip those switches up!

(you can use a multimeter to find out what switch power what wire…)

You might be interested in…

(We’re using the upfitter auxiliary switch #1 to power our Air Lift Spring Kit):

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About us



Hello! We’re Isabelle and Antoine 🙂 In 2017, we sold our house (and everything in it), quit our engineering careers, and moved into our self-built campervan. Every day is an opportunity for a new adventure... We’re chasing our dreams, and hopefully it inspires others to do the same!

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Thanks to all of you, we managed to negociate group discount on these. Strength in numbers!

10 thoughts on “Ford Transit Auxiliary Upfitter Switches | Wiring Guide”

  1. Many thanks! You make it seem clear and easy. Me with my big hands. I dunno. But I followed your file for taking off the A pillar and got my wires down to the glove box. Great for my 75 year old brain. Onward and upward!

    Your most non-engineer… 🙂

  2. The images and text were really helpful working on my 2023 van. It’s really a tight space behind the glove box. Thank you!

    My wires for the High Specification Vehicle Interface for the aux switches were different colors. I followed your diagram of the plug’s pins to choose the proper wires.

    The arrow in your image for the latch to the fuse box didn’t work for me. The one below your arrow did work. I could not get to the right side of the fuse box at all due to some other component. But I could open the case enough to see jumper F15 was set to B on all the time.

    I unwrapped the fabric tape and pulled out the wires I needed, then wrapped it back up. I didn’t want to mess with the original harnesses.

    BTW, on the other side in the engine bay there is a small oval rubber grommet that is a convenient passthrough to the area behind the glove box. It’s located between the large round grommet with a thick bundle of wires and the orange antenna cable grommet. I pulled the oval grommet out with some needle nose pliers and fished a wire through.

    It was also interesting to find behind the glove box the cabin air filter in the long horizontal box. I can imagine that will need to be changed once in a while.

    • I too have 2023 Van and also could not readily access the right side of the fuse box given its location. Please post any solution you find. Thanks.

  3. I have the 2019 transit and did not come with the upfitter switches, I purchased the switches and the pigtail for under the seat. could you please advise where the wire harness is located to plug into the back of the switches? I can not locate it
    thanks for all your info

  4. Bonjour Isabelle et Antoine.

    Just to share that I have a Transit 2022 AWD with the electric parking brake and found out that there is no such connector (C-33H) with that version. Not sure which option combo I took to end up with the electric parking brake though. I don’t mind as it is also opening options underneat but this mean that I will have to go the other route and access the other connectors behind the glove comparment. Just to share.

  5. Salut, J’ai trouvé un transit 2021 avec seulement une batterie sans l’option Upfitter… es ce que c’est possible de l’aménager pour installer l’alternateur? Par exemple ajouté une batterie? Merci

  6. Hi I have a 2019 transit. The upfitter switches look identical to the ones shown in the upfitter switch guard. I would like the purchase it but I wanted to know if you think the upfitter switch guard will fit a 2019, since the description says it for 2020+. Thank you.

    • Hi,
      The mating surface is slightly curved on previous Transit years (2015-2019) and the cover unfortunately doesn’t fit. I tried making a cover for 2015-2019 Transit but I couldn’t come up with a satisfactory finished product 🙁

  7. Hello Isabelle and Antoine!
    We have been inspired by your excellent van conversion site and adventures. We bought a 2021 Transit (WonderBus) and have been several camping excursions for over a year as work allows. Fantastic experiences! We are now getting some professional help with the simple “rolling tent concept” enhancement. We did order the Upfitter Switches and a wiring harness with the van. We are also curious about utilizing the switches for things like perhaps the MaxxAir fan or any smart moves for the 4 switches. Do you have any more insight into resources for the 2021 machine? Thank you!

  8. We have a 2021 arriving 9-15-21. Can’t find any infor about how to use the benefits of the dual battery, dual alternator, Upfitter Interface Modul, Upfitters Pkg that has modified vehicle wiring system, auxiliary Fuse Panel and how to use all of this to make it easier to add power to our van. Do you have suggestions, or know where we can get more infor. Thanks in advance., U


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