Far Cry 6 is massive, and there's plenty of things that will not appear on your map or HUD, and in We're (Un)Jammin' Yaram story, the McKay Wave Jammers are one of those things.
You need to find all 11 to complete the Yaran Story. Once found, all you have to do is climb the ladder and interact with the circuit breaker to disable them. One of them is destroyed as part of a story-related quest, but you need to find the rest for yourself.
All the Wave Jammers are found in close proximity to one another in the El Este region, in the La Joya area. More specifically, they are all clumped around Mirador Cape.
All McKay Wave Jammer Locations
McKay Wave Jammer #1
This Wave Jammer is destroyed in the Main Story Tourist Trap.
McKay Wave Jammer #2
This Jammer is to the southeast of the first, but this one has no ladder, so you need to grapple hook up to the platform.
McKay Wave Jammer #3
To get to this Jammer, you need to climb on top of the rightmost building. As you enter the La Joya Local PDP Offices, from the main gate, enter the door straight ahead of you, and the ladder is directly in front of you to your left.
McKay Wave Jammer #4
This Jammer is to the north-northeast of the fourth Jammer. This one also has no ladder, so you have to use your grappling hook to climb up to the platform.
McKay Wave Jammer #5
To access the circuit breaker on this Jammer, you have to climb up onto the red container at the side.
McKay Wave Jammer #6
To access this Jammer, you have one of two options. The first is by climbing up the hill to the west and using your wingsuit to glide onto the platform. Or you can use and find a helicopter/airplane and parachute onto it. There is an airplane to the east at the Gabriel Castillo Airport.
McKay Wave Jammer #7
To get to the platform, climb the wooden boxes behind the Jammer.
McKay Wave Jammer #8
To get up to this platform, climb on top of the wooden pallets behind it, to get o the container, then continue climbing.
McKay Wave Jammer #9
To access this Jammer, you need to climb the blue barrels on the west side of it.
McKay Wave Jammer #10
To get to this Jammer platform, you have to climb across the wooden logs, then on top of the two containers, then jump across.
McKay Wave Jammer #11
To access the last Jammer, climb up the ladder at the side.
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