。
I groped for the switch in the dark.
Literal
I [topic-は] darkness [possessive-の] inside [at-で] switch [object-を] groping-[manner-で] searched.
暗闇 (くらやみ, 'darkness, the dark'). 手探りで (てさぐりで, 'by groping, by feel') — 手 ('hand') + 探り ('searching') + で (means). スイッチ is an English loanword. A vivid tactile scene.