This is all I could dig up, I have the schematic on my boat but that is 900 miles away from here.
Dick
The original 4 button remote (+1,-1,+10,-10) had 5 wires, one common and the
other 4 command wires for each function. The later unit had 4 wires, +5v,
0v, sig A and sig B. The two signal lines had resistors to +5 and 0v to
have them sit at 2.5v when the buttons are not being pressed, then whne a
button got pressed, you got 0v or 5v on one sig line while the other sat at
2.5v until you got all four combinations.
I cannot remember which wire did what but it should be easy to work it out
once you know how it is supposed to work.
The big remote for the pilos that added auto/standby keys had a processor
inside and they sent data commands.
Regards