I'd be inclined to say wire length is probably the issue here, looking at your pic. Try shortening them up quite a bit. Power (pin 32) and ground dont matter, but the rest should be kept as short as possible. The way you have ground hooked up is fine.
Just to be on the safe side: - because I'm pretty sure, I read something about having to bridge the GNDs on both sides - I just connected Wiikey Fusion PIN 2 to a Gamecube motherboard GND PIN and left 4, 6, 8, 10, 12, 14, 16, 18, 20 blank.
Right side: like I connected it
Left side: like I thought, it had to be. Doesn't really make sense to me, but who knows... See this diagram from the tutorial
Since there was bridging "inside", I couldn't think of a reason, why I should bridge again or even connect every Wiikey Fusion GND PIN to the motherboard. Before I start soldering again, I'd like to be sure, the wire length is the most reasonable mistake. Excuse my precariousness, thank you for your help.
I accidentally got the wires for pin 26 and 22 mixed up and it still worked - but instead of waiting for the eject switch to be pushed, the wiikey automatically loads when the power is turned on. Other than that it seemed to work normally, games played fine and all. I'm not sure what's actually going on here, but it might be a solution if someone wanted it to function this way. I didn't try a 2-disc game while it was hooked up this way.. so.
This sounds like a useful discovery.
I think so, too. Is that reproduceable?