When {HEAD ~ the fifth wheel coupler} is connected to {TAIL ~ the pulley system}, the coupler can be moved into and out of engagement with the king pin 
is connected to
When { HEAD ~ the fifth wheel coupler } is connected to { TAIL ~ the pulley system } , the coupler can be moved into and out of engagement with the king pin
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH