Seatalk cables are just wires with I think it’s 1/8” female quick connects all moulded into a nice plastic shell. You can do the same - wire doesn’t have to be very heavy gauge. If making your own I would likely use 18guage stranded wire. If just doing data connection that happens on the two non-red wires. Red is the +ve power connection. You can feed power from autopilot end to instruments but shouldn’t feed power from instruments to autopilot.
For calculation of true wind speed and direction you need to feed the wind instrument BOTH boat speed (from depth/speed) and boat direction which comes from the compass attached to the autopilot. This last component is missing at the moment since the autopilot isn’t communicating with the other instruments.
Wind and speed/depth should be talking to each other right now, it’s just they can’t do anything with each other’s data at the moment. For a quick check you could try adjusting the back lighting on one - if I recall correctly this should adjust it on all instruments that are connected through seatalk.
For calculation of true wind speed and direction you need to feed the wind instrument BOTH boat speed (from depth/speed) and boat direction which comes from the compass attached to the autopilot. This last component is missing at the moment since the autopilot isn’t communicating with the other instruments.
Wind and speed/depth should be talking to each other right now, it’s just they can’t do anything with each other’s data at the moment. For a quick check you could try adjusting the back lighting on one - if I recall correctly this should adjust it on all instruments that are connected through seatalk.