Locking device for trailer hitch

In combination with a trailer hitch for connecting a rear end of a towing vehicle with a forward end of a towed vehicle wherein the rear end of the towing vehicle is provided with a support plate with a ball mounted thereon, the ball having a lower threaded portion projecting through and below said plate and being secured thereto by a nut and wherein the towed vehicle has an arm having a rear end connected to the forward end of the towed vehicle, the arm having a forward end which is provided with a socket for engaging the ball on the towing vehicle, the improvement which comprises a pivotal locking plate having a rear end and a forward end, the rear end of said locking plate having pivotally connected to the arm at a location between the ends of the arm, said locking plate being pivotal towards said support plate, said locking plate having a first hole therein adjacent the forward end thereof, the first hole having a diameter larger than the outer diameter of said nut whereby when said locking plate pivots into position so as to be against the underside of said support plate, the lower end of the ball and the nut will project through the first hole in the locking plate, a locking chain having a first end and a second end, said locking chain being attached at its first end to said locking plate intermediate the ends thereof and being adapted to extend upwardly around said arm and back to said locking plate such that the other end of said chain can be secured to said locking plate to lock said locking plate in position against the underside of said support plate.