"Tänker" sometimes means "think" but it also means "plan". The Wikipedia article states that it was illegal to make formal preparations to build a power plant, but even that was not enforced.
Even that… :)
"In Bill 2005/2006:76, the Persson Government stated the reasons for abolishing the law when it stated that there *had never been any ban on thought*, but that the "incorrect perception of the meaning of the provision is well established"
True. If your thoughts stayed entirely in your head then it probably wasn’t a crime. But if you for instance jotted down some rough cost estimates on a piece of paper you were in trouble. :)