A motor truck under s. 340.01 (18) (a) 1. registered as a farm truck under s. 341.26 (3) (a) may be used for personal and family purposes if the primary use of that motor truck is for purposes specified in s. 340.01 (18) (a) 1., except that a registered farm truck may not be used in furtherance of any nonfarm occupation, trade, profession or other employment, including commuting to or from the pla