The behavior of the function / sound buttons on a cab are not ALWAYS defined by the DCC system but can ALSO be defined by the decoder in the locomotive. To find out what button does what function, or triggers a certain sound on your locomotive, read the documentation that came with the loco, consult the company's website or contact them by phone.
On an NCE Cab per the NMRA standard:
The Bell button is ALWAYS the Bell and cannot be remapped
The Horn button is ALWAYS the Horn and cannot be remapped.
The F1 and F2 buttons CAN be remapped.
The Bell and F1 Buttons can perform the same functions or different functions depending on how the decoder in the loco is programmed or if you have remapped the F1 button to perform a different function.
For the Bell button, factory default is a toggle for F1 / function 1. The default is on / off with each button press.
To access the Set Cab Params menu:
Press the Program / Escape key (PROG/ESC) 6 times until you see Set Cab Params Press enter 6 times until you see Assign Bell to Function.
FYI- Older Soundtraxx Steam decoders use Function #3 for the Bell. The steam decoders can have the bell “re-mapped” to Function #1 (Diesel decoders can not re-map the bell to Function #3).
For NCE mobile decoders only, the corresponding CV information translates into:
CV33 F0F default value is 1 output 1 / white / pin 6
CV34 F0R default value is 2 output 2 / yellow / pin 2
CV35 F1 default value is 4 output 3 / green / pin 3
CV36 F2 default value is 8 output 4 / violet
CV37 F3 default value is 16 output 5 / brown or solder pad
CV38 F4 default value is 4 output 6
CV120 EFX for F0F output 1 / white / pin 6 default value is 1 directional active in Forward
CV121 EFX for F0R output 2 / yellow / pin 2 default value is 2 directional active in Reverse
CV122 EFX for F1 output 3 / green / pin 3 default value is 0 - standard on / off
CV123 EFX for F2 output 4 / violet default value is 0 - standard on / off
CV124 EFX for F3 output 5 / brown default value is 0 - standard on / off
CV125 EFX for F4 output 6 default value is 0 - standard on / off