You have found the difference in "stand alone" and "integrated" turn signals. When after market turn signals first came about, The dealer added turn signals lights to the front fenders(right on top and ugly as can be) Then they added them to the rear(often mounted to the rear bed post support). Can be quite interesting to see a truck with 2 rear turn signals and 1 Stop light. Dads truck had just this setup. When he bought a trailer, he got the tnegrated signal stat and the second stop light.
