High idle / SEIC to upfitter switches


Watch out for this guy
Oct 31, 2020
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North DFW
Current Ride
2020 F250 Lariat Tremor
Current Ride #2
2001 Ford Excursion, 2010 Ford Focus
I just finished up the high idle / SEIC mod on the truck. The third gen powerstroke wiring seems to be in line with the 2nd gen (2017-2019), so folks can presumably utilize the existing videos for those. For the updated documentation, you can reference the body builders layout book (https://fordbbas.com/publications) for your particular model year (thank you @Wanabxtrm). Technical information starts on page 110. The resistor table for both the 6.7 and the 7.3 can be found on page 121.

I did mine slightly differently than most others. For one, I didn’t create a “loop” for the resistor pack, but rather kept it cleaner by having the wires “touching tips.” Also, I didn’t use the pass-through wires. Those things are insanely difficult to get to. It was literally quicker and easier for me to run a wire through a driver side firewall grommet that I already installed. Of course, your own mileage may vary.

Here’s a quick rundown of how to do what I did.

  1. Open the cover on the passenger side footwell to expose a fuse box.
  2. Tucked in there is a pigtail for the PTO harness. Unplug it and pull it out.
  3. Find wire 9 (PTO RPM, green) and wire 10 (DIESEL PTO REF, white/brown) and pull the shrink wrapped ends off both (green circle).
  4. Strip a little extra off one of the two, then trim each wire. We're making one wire longer than the other.
  5. Solder on a resistor to extend the shorter wire so the other end of the resistor meets up with the longer end. The manual calls for a 1 watt rated resistor, but if you know ohm’s law, you’ll understand even a 1/8 watt will suffice. Just make sure you get a good quality resistor. I used a resistor pack to make roughly 19KOhm because I didn’t have a single 20k resistor laying around.
  6. Heat shrink the two wires together, so it looks neat
  7. Take wire 7 (PTO 1, yellow/green) and solder an 18 gauge wire to it. Heat shrink to protect the joint. Make sure you use wire #7 and not #14. For some reason, Ford used yellow/green for both. (You want green check mark. Leave the red x alone)
    IMG_20210104_075041.jpg IMG_20210104_075033.jpg
  8. Run the wire to the upfitter relay box in the engine bay. If you choose to go through the driver side like I did, you can run the wire around the glove box, through the center console, then around the driver kick panel. You can easily stick a hand into the center console from the driver side to fish the wire out. Well, at least my bony hand could. If you can't, I'm sure your wife can.
  9. Solder the wire to whichever upfitter relay you want. I did switch 1.
  10. Put everything back together neatly.
And here it is in working form
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Nice, I had done this on my 2015 and have planned on doing it to this truck but hadn’t gotten around to it yet. Thanks for the step-by-step.
Any idea of changes needed/ related to get it to work on the 7.3?

Quick google didn’t turn up a newer version of the SVE document referenced. But I did find this for the E-series 7.3... I suppose the values are likely the same. See ~ Page 47.

Anyone with fleet access able to pull down the updated SVE document above or super duty version equivalent below? Thanks in advance.

Since I’m fallen down this rabbit hole over lunch....it looks like these guys updated the instructions on their harness to reflect necessary changes to accommodate the 7.3.

Looks like their cost might just be worth the cost of entry to save some time running the wires; which is now been added to my to do list (and my truck hasn’t even shown up yet!)

Thanks for the distraction from work (though my boss may not feel the same!).

PS- admin’s the subject might be worth a sticky for future reference for us new guys!
Thank you its on my short list. (y) (y) (y)