Lionel KW Transformer question

As I interpret the schematic in the repair manual, and Lionel draws rotary switches in a screwy way, C is common to the 14 winding, the lamp, and the circuit breaker but also in series with the 6 volt winding whose common point is 'U'.  This is why with the throttle at zero you still have 6 volts on the track since the adjustment range for track volts is 6-20.  I would think if the trolley is running on a track that shares a common rail with the rest, you would basically short out the 6 volt winding with C and U, but if the tracks are totally independent as to all outside rails, including no crossovers, it would work.  You could also not use U at all, and just C, this would drop track volts to the 0 to 14 range with the throttles and eliminate the need to have a separation between a trolley track and mainline outside rails.  With C as common to all, that would let U give you 6 VAC for lighting or other stuff that could use 6VAC. D-C would be 14VAC steady,  and A-C would be 0-14.  Unless the trolley have a Lionel transformer operated whistle by the button, not sure what the loss of that extra 6 volts would do to that function, might not work unless you were at almost full throttle.