Finding studs behind 1" wood paneling?
If the thing you are mounting is wide (like a shelf or TV) it will cover a few small test holes. 

Drill a small hole through the board and lathe-and-plaster, then force a piece of bent wire through the hole into the void. The wire should have two right angle bends, one that goes inside the wall void and one that stays outside. The bit inside the wall must be shorter than the depth of the void, or it won't go in, but you also want it as long as possible to give you the maximum reach.

As you spin the wire, the end inside the wall will feel for the studs and you can use the other end to judge where the stud is.

If you can spin the wire right around, you know there are no studs within a few inches either side of your hole, so repeat the process double that distance to one side.

If the void between studs is full of insulation, this won't work. You may have to just drill holes every few inches until you hit a stud. You can reduce the number of visible holes by drilling diagonally in both directions,