If I had to guess, and it's just a guess on my part, it would be that the typical factory installed stalk on the steering column probably communicates first with the Ford Body Control Module which then operates the wipers on E-Series cutaways (and previous vans). Since the stripped chassis used on Axis/Vegas doesn't appear to come with windshield wipers from Ford, it's likely Thor buys the motor, switch, and wiring harness as a standalone system -- much like it was on older cars before electronics took over everything.
It may be possible to rig something that would work, but I doubt it would be easy. It's also possible these stripped chassis may not even have a BCM since there are no windows, door chimes, etc... like on a standard vehicle. There is no Ford body to control anything on. Again, just a guess on my part.
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