Adding a “Bell” to a Unit

[PullmanCar]

I have been using the “Grupo-Str” Ford F-250 Highrail and would like to add a bell to the unit. I have created a bell sound as a child and have that in, but there is no input mapper for a bell on the F-250 and I can find no input mapper in it (I assume it must use a RailWimulatorCore inoutmapper?). I have the bell sound child and files that I use for my bells (and it works on a different unit with a mapper for a bell) but how do I set a mapper for the F-250 to have a bell?

I would love any opinions or advise from the RWA Community on the topic.
‘PullmanCar’