Not to overstep my bounds by hijacking this thread but I went ahead and did the conversion on my 2000 so I figured I would share a bit. Bought a set of Dorman 620-422 replacement fans for the 2010 Expedition. I contacted Dorman regarding the current draw of each fan and they stated each pulls 25 amps. One is 14.5 in., the other is 15 in. They pull 2800 and 2900 cfm respectively. Thank you Rob at Dorman support for that info.
Regardless, I gave each fan it's own relay to split the load and wired both to always be on at full speed when the ignition is on. I didn't feel like wiring these into the A/C circuit at the time and my luck with the temp sensors provided in fan controller kits hasn't been great. Plus, I've upgraded to a 200 amp alternator with an overdrive pulley so I felt fairly safe that it could handle it even at idle. However, I bumped the idle speed to 715 RPM which puts the alternator at an output capability of about 125 amps. Thanks to Powermaster for the alternator dyno sheet.
So the passenger side fan runs flawlessly, no issue with a 30 amp relay and circuit breaker. The drivers side has caused some issues however. The continuous amperage seems to be above 25 amps as it consistently popped a 30 amp circuit breaker. I upped both the relay and circuit breaker to 40 amps and it is able to run continuously fine. However, I suspect the start up amperage spike is quite significant as over the course of a month or two it will fry the 40 amp relay. As far as I can tell it doesn't pop the circuit breaker. I'm an amateur when it comes to electrics so I'm still working all this out.
Nevertheless, I'm currently looking at either wiring in a resistor traditionally used for the old taurus fans (which I read somewhere could spike at 70 amps during startup) in order to drop the current or using a pulse width modulator motor controller. I'm leaning towards PWM since it gives me a wider range of control. Once again, I'm an amateur so electrical engineers feel free to chime in. Additionally, if anyone knows how the 3rd Gen Expeditions control these fans please let me know. I haven't been able to find any information on it so far.
Anyways, I know this thread is on the 2nd gen part of the forum but hopefully it still provides useful information for anyone looking to do this.