**** SAFETY GOGGLES REQUIRED!
1) Set headlamp housing down into the ring
2) One "end" of the spring you'll hook up into the curled lip of the ring, with the "bendy bit" down against the lamp as the above picture shows.
3) Using fingers, pliers, etc mash down on the other end of the spring, forcing it "wider" and then hook it up into the lip of the headlamp.
4) Repeat until you've got it clipped all around.