Looking at the wiring schematic, the mode switch (S4) has a resistor symbol inside of the block with the switch. The description of the switch under "Display Mode Switch Circuit Operation" (page 256 or so) just says that when the switch is depressed, power is supplied to the ICC. It's not clear what the resistor symbol is for, I'll guess that it's a simple divider which insures that the +battery that goes in comes out as 5V or something. Nothing is said about what the voltage on the open wire (908, gray) that goes to the switch would be when the switch is open. BTW, the battery is on the red wire going into the switch.
The turn signal switch just feeds switched battery into the ICC, no resistors shown. All this might be as simple as what inputs where averrable on the ICC, and perhaps some were 5V input and some were +12 inputs.
The mode switch comes off of the key switch, so if the tractor is off the switch will not draw down the battery.
I would think you could put a meter on the switch and see things change as the switch was toggled to help determine if it's the switch or a wiring problem. I belabor the point about the resistors so that it's very clear that shorting out the switch at the contacts is probably a bad idea, since it would send 12V into the ICC so be careful when making this measurement.
Another "clear as mud" post....
Pete
