How does a A/B printer type data switch work?

My question about the data switch is when you switch from A to B does the switch completely switch all conections with A and create new conection with B, or are there still some contact such as common wires still connected?

Thanks in advance
Bob

Pins 18 - 25 of a printer port are all connected to GND, these are all connected together and not switched...

As for the other pins 1-17, these are switched between outputs
So in position A pins 1-17 from input are switched to pins 1-17 from outputA
And in position B they are connected to outputB