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 by searching ovens (found in many abandoned houses, for instance in Minefield), or they may also be found in some 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.

Fallout: New Vegas
This item is not used in any recipes, but is used in the quest, Not Worth a Hill of Corn and Beans, which requires 2 pilot lights.