Why not 8 for good measure!

My house was built in the 70s, the studs were 24" on center.

My house was built early 80s and studs are 24” apart.

I installed security systems for a summer, and we had to drill a finger-sized hole behind the panel to drop the wire down the stud space to pop out at an outlet for the plug. I was having the absolute worst time getting the pull, ended up with a palm-sized hole (still fine, it would be hidden by the panel) and couldn't make it. With the customer's blessing, my manager (who had come to find out what was taking me so long) cut a hole big enough to look inside the wall. The framer had decided to slant a stud from bottom left to top right of the "cell" for some idiot reason, and the angle was slight enough that we couldn't sense it by touch. Moral of the story, don't trust that the framer from a full sixty years ago did what they were supposed to do, or that nothing has been changed since then.

Fun fact. My house was built in 1939. The guy who built my house must not have known about 16" on center, he also didn't own a tape measure. Or a level haha

They can be 24” OC, especially in older buildings.

If you're hanging the TV odds are very slim of hitting any wires.

Aren't electrical wires close to them?

If the building is original and hasn't been renovated, then the studs could be anywhere from 12" centers all the way to 24" on interior walls due to the age of the building. I've seen some with 4 foot centers as well.

Hit the studs and you won't hit any electrical wires - it's really that simple.

Find an electrical outlet. They are nailed to a stud

Im not really understanding what your describing , do you have a picture as an example?

I used strong magnets hot glued onto a long string and just kind of moved it along the walls. When it froze, that's where my stud was. Then I made a mark on the wall and kept going in order to mark where the whole stud might be.

Check for nail holes in the baseboard, especially if the nails holes are higher that about 1.5”.

I have a similar one to this and it works great, it finds the drywall screws which SHOULD be in the studs.

Remove the mulch down to bare dirt. Over time the mulch will decompose and the shed will settle on you.

Cut one of your top boards in half, so on the bottom you have 2 8 footers, and on top you have a 4, then the 8, then the 4 footer. That will stagger your joints.

You could also drill through both Timbers, and pound some rebar all the way through into the ground. (Drill at least 6 inches from the end of the Timbers to prevent splitting.)That would be the best way to tie the Timbers together, and to anchor your frame to the ground.

From what I’ve seen, cable is threaded through holes drilled in the studs, so you would not hurt the electrical cable. I have hung three TVs and have never had a problem. You can also buy cable management at a big box store to hide any cords and HDMI cables from your newly hung television.

This, do this.

You can pull the baseboard off, if it’s fairly easy and use nails to figure out the spacing then put it back in place. Just a thought.

Right. Someone else here mentioned it: locate a power outlet. The electrical box for them are nailed against a stud, which is either on the left or right side of the box, so you only need to try two positions with a nail to find a first stud. Then measure in 16" multiples to locate the rest.

I have no experience with them but I'm told that there are smartphone apps which will do this.

Definitely take it back to hard dirt. Good firm base, not going to rot away and sink down.

Even if it is a true corner, the wall in question might also start behind the adjacent wall so the center of the first reachable stud will be about 12.75” from the corner (assuming 1/2 drywall)

Measure from a door jam to your closest outlet. That will give you a ballpark rule by division.

Your walls wouldn't happened to be plaster and lathe, right? It would be extremely rare for a home built in the 60s to be built that way, but who knows.