pivot pin 65 having an axis c and supporting arm rest at 66 control member 27 39 terminates downwardly in supported attachment to a universal coupling such as that shown at 30 in the first form of the invention to permit the modified control member 27 39 to move in like fashion about axes a and b a portion of the modified control member additionally moves about a horizontal axis c the control member 27 39 also includes a handgrip 69 and a forward arm rest 70 from which an extension 71 depends with a sleeve 72 fixed thereon a grounding or 34 kill 34 switch 73 is housed within extension 71 and is of the spring return type with normally open contacts which may close upon release of control member 27 39 to establish a circuit to ground to interrupt the ignition circuit of the vehicle engine slidably carried within sleeve 72 is a block 74 which acts on a switch button 75 a helical spring 76 biases block 74 and hence stem 75 downwardly to the switch opening position of fig7 during vehicle operation the operator 39 s arm at rest on control member 27 39 urges said member downwardly about axis c resulting in switch 73 being open to permit continuous engine operation accidental or intentional release of the control member permits spring 76 and an internal switch spring not shown to displace the switch upwardly from block 74 resulting in closure of the switch contacts to disable the vehicle.