Get a cheap temp sender from a 06 model, buy (local plumbing supply) a brass pipe T and 2 pipe thread to hose barb fittings. Insert in series of one of the rubber water lines. Be sure to run the gauge ground to the T.
KHB1

Sorry i dont have any info on the electronic body module. My truck spent two weeks at the dealer garage. They changed the thermostat, temp sending unit, instrument cluster as well as the wiring harnass. Nothing worked. I made a few phone calls and spoke to the leading authority on Fords in South-Afica who told me that we need to replace the module. It was done in 10 minutes and cost the dealer R 450 (that's around USD 55.00 ).
If you continue to battle let me know and I can try to get a part number or pic.

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2006 4.0 XLT Auto 4x4

I have a 2002 2.3L DOHC and finally got fed up with the lack of temp control from the thermostat with the electric heater (common to 2001, 2002 and 2003 Rangers with the 4 cyl engines). I replaced it with the non-electric assembly used in 2004+ Rangers and paid ~$30 on Amazon. I saved ~$100 and fooled the computer by adding a 1200 Ohm 1/4 Watt resistor across the two connector leads so it doesn't show shorted or open. There is no CEL and the temperature now heats upo quickly and remains constant on the gauge. The old thermostat had failed: the seal around the valve seat had ripped, the plastic directing the heat had cracked and the electric heater was corroded.