The first Tallneck you’ll come across, and the easiest the climb. Run up one of the nearby buildings on its route, although keep an eye out for Watchers, and leap onto its back. Once there, just hop between the platforms to reach its head and Override it.
This is a little trickier than the first Tallneck, largely due to the fact that its patrol area is a around an island that is almost exclusively populated by Snapmaws, with the occasional Redeye Watcher - the Watcher’s big brother. You’ll need to swim across the water, Snapmaws patrolling all the while, then use one of the cliffedges to leap onto its back. It’s best to avoid a fight if you can because the energy pulse from completing the Tallneck will damage or kill everything around you anyway. When you get on top of it, climb up and do your thing.
This Tallneck is in the desert area and surrounded by a camp of the Cultists. There are a few corrupted machines, a host of human enemies and a corrupter in the area, making it a dangerous one to approach without a level of caution. Stealth is definitely the best option. You’ll need to get up onto the ledge that runs around the back half of the area to find the platforms that will allow you to jump onto its back. There are multiple humans patrolling this ledge though, so either kill or avoid them until you get to a ledge where you can access the Tallneck, then leap aboard and climb your way to the top. The pulse this Tallneck gives off will also kill all the human enemies in the area, so clearing them out is a little pointless.
This Tallneck is in a wide open space filled with Ravagers, Longlegs and Watchers, which provides ample opportunity for getting outnumbered and overwhelmed if you’re not careful. Luckily, there’s a decent amount of cover provided by the rocks scattered around this sandy area, so use those to your advantage to approach a ledge you can use without being seen. A Watcher may be patrolling on the ledges that will allow you to jump onto the Tallneck, if so, take them out then jump onboard to get this one in the bag.
The last Tallneck patrols in the south of the map, in the jungle. Once you find its route, you’ll have to contest with a number of patrolling Longlegs and Watchers who guard the raised path that will allow you to get onto the Tallneck. Longlegs are tricky customers, but the best bet is to use Tearblast arrows to get rid of their jumpjet ability then use Precision or Hardpoint arrows to hit their sonic pouches under their necks to do big damage. When you get a clear run at the Tallneck, leap aboard and that’ll be the whole map revealed for you, plus all the datapoints that come with the Tallnecks.