Pilot Light (Fallout 3)

The Pilot Light is one of the several scrap items that can be used in the construction of weapons and ammunition using schematics.

Locations
You can easily find these either by searching ovens (found in many abandoned houses, for instance in Minefield) or sometimes they are found in workshops. A pilot light can be obtained early in the game by searching through Silver's stove inside her house in Springvale or in the RobCo Facility.