Mystery Switch on TMCC locomotives?

[Kerrigan]

On our Weaver Little Joe, which has TMCC, there is a switch which has two positions "Signal" and "Full".
Does anyone know what this switch controls and what the two settings mean?
I have this same switch on two other TMCC non-Lionel engines, and not a mention of it in the instructions or TMCC manual that I can find.
Thanks!

[chuck]

Sound Control.  Signal means "Signal Sounds", just Horn/Whistle and Bell.  Full means full RailSounds, aka engine noises, brake squeal, TowerCom/CrewTalk (if available), coupler, yada, yada, yada.