The OTC uses the hot from the transformer to terminal 1, which powers both control rails. Terminal 2 connects to the center rail, if needed. The ground is via the rails. The barrel unloader, twin dump and horse cars take advantage of this, but no other operating cars can unload with just one OTC. (It is possible to use two OTCs to achieve normal unloading by spacing them accordingly and connecting one to ground). Note that an energized OTC will operate slideshoe coil couplers.
The UCS is complicated- in the uncouple position, all control rails are powered by the (hot) center rail, in unload, half are (hot) center rail, half are (ground) outer rail. Left to right, the first screw is outer (ground) rails, the second is both control rails left of the magnet, the third is the (hot) center rail, and the fourth is the control rails on the right. For constant voltage the third wire to the controller is connected to the transformer directly and the third screw is not used.