retrolefty:
In the electrical word this is accomplished by 'interlocking' the relays in question ... and the other set of contacts opens the coil circuit of the opposite relay, thus preventing the possibility of having to relay coils powered at the same time.
Fair enough, but totally unnecessary in this case as the SPDT contacts simply switch the motor correctly in all cases.
If only people would read the link which explains this.
Hmm, let me see what I can do ...
http://static.howstuffworks.com/flash/power-window-schematic.swf