Knowledge Note KN1048
Car PC JoyCon Exr/Exd
Block Channel A by Channel D

Block CH A by CH D option is useful when you use a stalk adaptor(eg. PAC) by ACC power but the car PC is powered by its own battery. The signal from the stalk adaptor is undetermined when the ACC is off. But PC is still powered by its own battery. So JoyCon need to ignore the undetermined signal from the stalk adaptor after the ACC is off.

To use Block CH A by CH D option, connect ACC to Channel D.
Put the D1 button bar to the ACC OFF side and put the D2 button bar to the ACC ON side.
When the ACC is on, channel A signal is processed as normal.
When the ACC is off, the indicator of Channel A moves to the right most side and all the signal to the Channel A is ignored.

https://www.exinterface.com/d/an/1048/KN1048-(CPJexr,exd)Block_Channel_A_by_Channel_D.pdf