IIRC, *ALL* 99+ Windstars use low-side switching for lighting. You can check the van for where it was manufactured - but *ALL* Ford Windstars were assembled at Ford's Oakville, Ontario plant - so assembly location isn't really the issue.
Yes, you'll need to convert 99+ Windstar lighting signals in order to connect trailer lighting. You can do it with an electronic conversion box - or use relays to accomplish the same thing, as noted above.
I went overboard wiring my Windstar for trailer work: I added an electronic conversion box with its own power source (it uses van lighting only for input; the power to drive the trailer lights is separately sourced, with its own fuse). I added a high-current, relay-controlled 12V line to run a refrigerator in a popup camper. I use a Tekonsha Prodigy brake controller; it has associated wiring to run electric trailer brakes. All of these circuits have *their own* fuses.
I also added an auxiliary transmission cooler to my Windstar, which I highly recommend.
I took a number of pictures of my Windstar towing-related projects. See links below:
Adding popup camper brakes
Adding Airlift spring airbags to a Ford Windstar
Ford Windstar tranny cooler, wiring and brake controller