How do I plant the sensor on an electronic transformer. The only one I've seen is in the meth lab next to Kenny's house but you cant climb the ladder inside. The wall above the ladder sparkles but you cant shoot it!

It's shootable. I've done it in both of my playthroughs. Reload from an earlier save?

Go inside the tweakers lab, head up the latter. You should see something glinting in the upper right hand corner.

Shoot it, it should destroy some parts in your way and you should be able to climb the latter up.

Hit it with a melee attack, and it will break.

Other is top of barn.

Other is a sign far left of town