I found a sensor icon in my Inventory Missions, but I have tried every way imaginable to "plant" it at or NEAR the sensor markers on Yavin 4. What is the specific method for planting these things, once we've found the markers?

You need to click the sensor marker on ground, that it will make your character to put the sensor on it automatically.

I've left-clicked and right-clicked the marker, the ground surrounding it, the Jedi Knight, the companion, and just about everything else, but nothing happens. What am I missing?

did you try relogging?

I've tried relogging, quitting and praying, but nothing works. Actually, two have worked, where I was able to plant the perimeter sensors on the round huds, but nothing works for the remaining four. In fact, I don't see any markers for where they might be in all of the Yavin maps. I think I found the first two by sheer luck, but as mentioned, nothing works when I stumble upon one of the remaining four huds. Edited February 11, 2017 by quinn_shandess

You must be on the right mission to do this. It's either the quest mission when you arrive on Yavin IV or the daily. You can find the sensors in the 2 eastern zones (3 each) and 5 "secret" in the adjacent caves (for the achievement). Furthermore there is one sensor next to the imp/rep-base at the second waypoint (for another achievement).

 

http://dulfy.net/2014/12/02/swtor-yavin-4-achievements-guide/#No_Sensor_Left_Behind

I've tried relogging, quitting and praying, but nothing works. Actually, two have worked, where I was able to plant the perimeter sensors on the round huds, but nothing works for the remaining four. In fact, I don't see any markers for where they might be in all of the Yavin maps. I think I found the first two by sheer luck, but as mentioned, nothing works when I stumble upon one of the remaining four huds.

 

Yeah, there are issues regarding the quest objective markers (yellow triangles with green center) not showing up correctly on the larger map. The icons only show up reliably on the minimap circle in the lower right corner of your UI by default. However, once you realize this bug the beacons will always be marked by the mission triangle marker and are always at those locations. The six for the daily mission are in the Verdant Swamp area for the republic and the similar zone (I'm blanking on the name of the map zone) in the south for the Imps. They're the two zones on the most eastern side of the Yavin map, that get joined by the cave network into the central area which has the imperial guard training grounds shared by both factions. Any other sensor beacon you come across, usually in the cave network, are part of that hidden achievement, and not your mission.

 

Basically I quick travel to the taxi in the imperial guard training grounds, speed to the opposite faction zone to click on the three posts there, and then quick travel to my faction's taxi on the opposite zone to hit the three there.

 

The relogging workaround is most reliable if a mission object is invisible, but if the object is visible to you and cannot be clicked it is possible that someone came by recently and clicked it before you. If they are clickable for your mission, they will just appear as glowing blue disks on the ground. If they have a cylinder on top of them then they have recently had a beacon placed on them by another player and you have to wait until the cylinder despawns.

Thanks very much, phalczen, for suggesting the minimap to locate the sensor hubs. I hardly ever looked there – until now, that is – but that sure solved the problem. Why they couldn’t be indicated on the main map is just another SWTOR mystery. Please stay tuned to this “Missions” Forum because I’m just starting on Yavin 4, and I’m sure I’ll have more questions. We need knowledgeable players like you to help clueless players like myself. Again, many thanks, and thanks also to the others who responded.