The motorized valve is very different from the solenoid valve.
The motorized valve shuttle is moved by a DC micro motor that only moves when the control polarity on terminals D & E changes. The valve incorporates an internal limit switch with diodes. The limit switch cuts power to the motor once the valve shuttle has reached the end of it's travel. It retains its' position till the control polarity on terminals D & E is reversed.
Micro ISO relays have an energized and rest position for the internal switch. They don't retain their switched position without power to the coil + terminal #86.
The dash switch is on ignition power so the relays in my diagram will go to the rest position when the ignition is switched off.
If there's power present on the Red +12v wire in the diagram the valve will spin to the MAIN position just as if you flipped the dash switch to MAIN.
I've been intending to do a tech writeup on the two tank switchover systems on the 73-91 CK RV trucks...
Here's a couple graphics from that incomplete effort that may help you visualize what's happening in the motor type valve.
Here's a cutaway of the motorized valve from Pollack.
Internal Switches in Motorized Valve
