You stated you disconnected the Red Sea talk wire at the computer yes? That wire supplies power to the “auto pilot control head”. With it disconnected no power goes to the control head or any of the other instruments if you just turn on the “auto pilot switch”. Power will go to the computer, but no further. It is the “autopilot computer” side you are isolating as it provides the power to the motor and takes the most power.
If you turn on just the “navigation switch” it will provide power to the wind, speed/depth and the control head but not to the autopilot computer - control head will act as a repeater for some information (wind/speed/depth) but won’t do anything with the auto pilot as it’s not receiving power.
Further to the right from the seatalk connection on the autopilot computer will be two heavier wires one going to the “autopilot switch” the other going to the negative buss. - it is this connection that provides the power to the computer, drive motor etc.
As mentioned above you could just put in a grey and yellow wire between the depth/speed and the autopilot control head, then reconnect your red wire at the computer. Either this change or how you have it currently should work as long as the “auto pilot switch” is turned on last. - it seems, at least on my system, that the other instruments don’t care if seatalk is running, but the autopilot is smart enough to know it’s connected but not “functioning”.
If it would be less confusing for you - you can change the system to a single switch - but power must be supplied only from the autopilot end. - you would re-connect the red wire at the autopilot and disconnect the non-jumper sea talk connection on the wind instrument.