Just how do load equalizer trailer hitches work?

Answer 1

try this http://www.mrtruck.net/wdh.htm

Answer 2

Equalizer Trailer Hitch

Answer 3

Referring to the pictures in answer 1: instead of just resting on the ball of the hitch as with a simple trailer, the load equalizer preloads the connection by pulling up on spring arms that go under the hitch pole(s) of the trailer and attach to it(them). These are pivoted at the hitch (underneath) so they move from side to side while the springiness allows up and down movement.
When a trailer is put on a ball, the vehicle back end drops more or less depending on the load. When an equalizer hitch is connected and loaded, the back end actually rises to level, because the load is shifted to the front wheels by the forward point arms pulling down. Besides keeping the vehicle in proper driving position (level, not nose high), the connection is stiffer because of the friction at the joints under the ball, not just the free movement of a ball.
There was a famous picture of an Olds Toronado front wheel drive sedan and a heavy boat trailer with an equalizer hitch where they took the rear wheels off the car (and wired up the axle) and drove (in a straight line) to show the hitch taking all the weight of the back end of the car and the fore-end of the trailer.