I have driven and worked on a truck with a US gear unit. They are very robust units to say the least. I may be wrong, so don't quote me on this. It has a spring that makes it engage correct? I didn't think it had a motor, or solinoid to make it engage. I've been using GV for many years and love them. But they are not as stout as a US gear. Which has been out of business for a while.
Anyway, I thought that there was a tension spring that gets put under pressure by the rotation of the unit, and a solinoid allows the spring, to "spring" and engage the unit. I may me waaaaaay off on this. But then again, I've never looked at one outside the truck, or an exploded diagram...... Google here I come.
