855 control lever????

[Stama]

Hi, have just recently been given an 855 with loader and backhoe attachments. The tractor had been sitting around for 5 years at my work yard and not used so my boss let me have it. Obviously there is no manual for the machine. I have figured out all the controls as I started working on it yesterday except for one lever. There is a lever with a red ball knob on it that sits up on the left hand side of the seat. Only does one click back or forth and have not noticed anything change when operating it. Can someone tell me what it does please????? Thanks in advance

 

[F-I-T]

4 wheel drive in and out.

 

[Stama]

Thank you!