the flat spring 48 are thus rigidly interconnected by the fastener 50 the arm 46 and spring 48 in turn are pivoted by a common pin 54 to a support bracket 56 mounted on a seat plate 58 the pivot arm 46 extends through a slot 60 in plate 56 and connects to the remainder of system 40 the lower end of the other seatbelt portion 36b is secured by a fastener 62 to a bracket 64 which is anchored to plate 58 by another fastener 66 it will thus be understood that one end of the seatbelt 36 is secured to a fixed bracket 64 while the other end is attached to a pivot arm 46 brackets 56 and 64 are laterally spaced apart and preferably located well back with respect to the operator seat 22 so that pivotal positioning of the pivot arm 46 will vary in accordance with whether the seatbelt 36 is properly fastened the position of the pivot arm 46 in turn controls the locked or unlocked condition of the remainder of system 40 as will be explained below referring now to fig4 and 5 in conjunction with fig2 the lower end of the pivot arm 46 is pivoted at point 68 to one end of a rigid link 70 the link 70 extends through an opening in a bracket 72 and a compression spring 74 is provided between the bracket and a follower 76 on the bent link for purposes of normally biasing the pivot arm 46 backward relative to seat 22 the other.