The retangular headlight are used on the older style (pre Crenlo cab) machines. Both headlights are similar in size however the newer (1997 and up) machines take the 517372 light. This light has a snap action 3 pole connector.  The 516572 and 516573 headlights are a rectangular shaped light with an amber signal lens and were mounted on the front corners of the Terra-Gators, either on the fenders or frame brackets.