My Garmin has one channel with Brown/Blue (Blue is Tx out)
And the other with Green/White (can't remember offhand which one is which at mo)
When I had the silva fitted I used the Brown only from the sounder input and the blue only as the output to the VHF with the 2nd channel switched off. I intended to eventually use this to link to a Magnetometer (when I have the £2k to buy it)
I found last night that connecting the Icom the original way didn't work, nor with one wire on the second channel, it would only take a position with both wires connected (+ and -). So it is now connected to channel 2 with both wires.
I am not worried about it too much, I can't afford the magnetometer for a long while yet