Ford MAP/BP Sensor Operation and Testing
I did some reading and simple calcs and came up with the same thing as your testing. It looks like if youve got a stock cruise control, and your cruise control gets in the neighborhood of 8000 PPM like a lot of vehicles here appear to, you could just substitute the speed signal for the Ford map sensor signal. Have a switch to go between speed sensing and load sensing.
My cruise module sends a 12v signal, and senses when that signal is connected. So looks like I would need to have the Ford map sensor pulse a transistor rather than send the voltage direct to the cruise module.
This would work well in the van, at 8000 PPM. My cars are 4000 PPM, which may or may not work. Substituting a cruise module from a junkyard van into the car may work, Id just about bet theyre the same thing except for the PPM they receive.