[ElectricMotorcycles] Brother-in-law button?

[Johnathan Vail]

I deleted the email before I got back to the browser to see the diagram 
but what is the function of this button?

http://electricmotorcycles.net/modules/xcgal/albums/userpics/10003_massupload/ebike_wiring2_sml.jpg


jv <- Hells Amperes Motorcycle Club