I just spoke to Equalizer Systems - they said that there's a pin switch (small, pushbutton) mounted on the stationary part of the retraction arms. He wasn't sure about whether it was the front or rear arm but he said that's what is responsible for switching over from the hydraulic retraction to the slide locking circuit. I'll look for that switch sometime in the next day or two and update if I find it.
I know these rigs are sort of rare, but if my trouble and resolution can help someone else, it costs me nothing to put it out there.
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