On ALL NCE cabs The "F0" (the actual 0 key) and "Headlight" keys are identical in every way. In fact they are hardwired electrically as such.
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
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