If you have a Police Interceptor Utility, there is no wiring harness under the trim piece. I am going to test whether or not Tow Mode even is programmed into the transmission.
Tow Haul comes off of the BCM, to the momentary switch, then to the Transmission Module. The PIU's Low Gear column switch comes off the BCM, to the column switch, then back to the Transmission Module. Both Tow Haul and Low Gear go to the same pin on the Transmission Module. They come from different pins on the BCM however.
When I test this, either I blow something up, nothing happens, the Low Gear option gets activated as usual, or Tow Mode turns on and functions.
Apparently no one has tried this yet.