Professor Layton and the Diabolical Box

Puzzle 112: Turn On the Light

Original diagram for Puzzle 112: Turn On the Light

A light stays on whichever pair of its three contacts you touch together, so how is it wired?

Chapter
Chapter 5
Location
Museum Gate · Duke
Picarats
40 picarats
Type
Write Answer
Region
Same in all versions · Also called Turn on the Light in Europe
Hint 1: A gentle nudge. Tap to flip.
Hint 1

Think about what 'stays on' really means.

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Hint 2: The key idea. Unlocks after the previous card is flipped.
Hint 2

If the light is on for every pair, is there any situation where it's off?

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Hint 3: Almost there. Unlocks after the previous card is flipped.
Hint 3

The contacts don't matter at all. What's the simplest circuit that keeps a bulb lit?

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Answer: See the answer. Unlocks after the previous card is flipped.
Answer

The answer is wire the bulb straight to the battery, with no connection to the contacts.

Tap to flip back
Solution, FAQ and sources

Solution

The light is on whether you touch A to B, B to C or A to C. Nothing about the contacts changes anything, so the light must simply be on all the time.

The simplest wiring is to connect the **bulb directly to the battery** and leave the contacts unconnected. That uses the least wire, and the bulb stays lit no matter which contacts you press together (or none).

About this puzzle

On a simple board, touching contacts A and B together switches a light on. A second board has three contacts, A, B and C, and the light stays on whichever pair you touch together. Using as little wire as possible, how is the second board wired underneath?

Unofficial fan guide, not affiliated with LEVEL-5 or Nintendo. Puzzle description, hints and solution written by Hint by Hint.

Similar puzzles: Puzzle 113: A Stack of Dice, Puzzle 109: Walking the Dog, Puzzle 152: The Card Tournament, Puzzle 111: How Many Turns?

All Professor Layton and the Diabolical Box puzzles

FAQ

What is the answer to Puzzle 112, Turn On the Light, in Professor Layton and the Diabolical Box?

The answer is wire the bulb straight to the battery, with no connection to the contacts.

Where do you find Puzzle 112 in Diabolical Box?

Puzzle 112 appears in Chapter 5, in the Museum Gate area, when you talk to Duke.

How many picarats is Diabolical Box Puzzle 112 worth?

40 picarats.

What is Puzzle 112 called in Pandora's Box?

In the European version, Professor Layton and Pandora's Box, it's called Turn on the Light. The puzzle itself is the same.

Sources

Facts checked on November 14, 2026

Unofficial fan guide. Not affiliated with, endorsed by, or sponsored by LEVEL-5 Inc. Professor Layton, The New World of Steam, and all related names, characters, and trademarks are the property of their respective owners.