Dead Island Side Quests Walkthrough: On the Air

You get this quest from Dominic in the lifeguard station. It is needed to complete this in order to advance the "To Kill Time" main quest.

Dominic asks you to  go to the lighthouse and get a signal amplifier.

Take the truck (Assuming you've done the "Lazarus Riding" sidequest) and follow the road to the lighthouse. Make sure to run over zombies on the way, to get some extra experience.

When you get to the lighthouse, Talk to James (on the balcony)  who will ask you to help out people around the lighthouse. Then talk to Darvin and do what he says to complete the "A Ray of Hope" quest to gain access to the room where the signal amplifeier is. See our Ray of Hope Walkthrough

Once you've completed A Ray of Hope, Darvin will let you enter the storage shed where you will find the signal amplifier. Take it and bring it back to Dominic in the Lifeguard Station to complete the quest.