The torch you find from the van is broken. Look at the torch in your inventory to get a hint.
This is the low-spoiler guide for "Fix the torch" puzzle in The Darkside Detective - A Fumble in the Dark. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.