The plastic insulator has bayonet pins that fit the rear of that socket. just like the bulb. Once it is installed from the rear and locked with the bayonet pins, it's spring loaded contacts are ready for the bulb to be inserted in front. The pins of both the bulb and the contact insulator hold them in place and key them, so that bulb contacts align with insulator contacts. The boot fits over the stick out brass receiver. 1157 is the correct bulb.
Jim carter, who sells that light in pairs, shows a pic with wires included? Did you get the wires????? He shows a metal rear contact/wiring scheme. Contact them for suggestions on the part you need.
