Cid asks you to help jam the Imperials' communication signals, to delay their discovery of a missing magitek armor.
This quest is available if you have completed the quest Getting Even with Garlemald, and have reached level 46.
Starting the Quest
Talk to Cid in Revenant's Toll in Mor Dhona to begin the quest.
Use the Electromagnetic Reader
Go southwest to leave Revenant's Toll via the southwest gate, and go to where the orange arrows are pointing in the minimap. You will find five Prime Locations in the area. Some of them are glowing purple (enemies will appear when you use the reader on these), but some are just sparkling. Dismount and target each one, and then you can either examine or target them and use the Electromagnetic Reader on them from the Key Items section of your inventory, or you can target them and use the icon to the right of the quest name in your list of active quests.
One of the five locations is at the top of a slope within the large crystal. The base of the slope is on the east side of the large crystal formation. Go there and make your way southwest up the slope to find the Prime Location at the top.
Report to Cid
After you have used the reader at all five locations, go northeast to Revenant's Toll and talk to Cid to hand over the Electromagnetic Reader and complete the quest.
Next Main Scenario Quest
After you complete the quest, talk to Glaumunt to accept the quest Acting the Part if you haven't already. If you have already completed it, talk to Sark Malark to accept the next quest: Dressed for Conquest.