It appears that the St40 series only has a single connect on it so you can not daisy chain like the St 60 series. If you are good with wiring, you could splice the cable wires together. I did that on adding ST50 to ST60 instruments. They have different connectors.

 

But I should be able to get True wind speed from the st40 right?
I guess I'm confused about where I'm splicing the cables. I understand that the Wind instr. needs a boat speed input to calc it, but I'm not sure which cable I'm splicing. Does the interconnect kit allow you to 'plug and play'?

 

The raymarine cable is :
gnd black
12 volt power red
seatalk yellow
shield silver, bare wire

Information between instruments is shared on the seatalk connection.