MIL-DTL-25866C
3.13 Power failure relay. The light shall be provided with an approved relay, which has
a set of normally closed contacts. The coil of the relay shall be energized in the armed position
from the aircraft electrical power circuits (28 volts direct current (VDC)). The operation of the
relay shall be such that whenever the aircraft electrical power fails or is turned off, the contacts
will be closed and the lamp will be automatically energized from the self-contained battery
power supply.
3.13.1 Rearming circuit. The light shall be so designed that it can be rearmed by the
light switch, and remotely rearmed if so connected. Figure 2 illustrates a circuit by which this
requirement may be obtained. Other circuits will be acceptable provided the requirements are
met. If the light is to be de-energized and rearmed remotely, the control switch shall be
connected to terminal C.
3.13.2 Electrical connections. Four 8-32 screw-type terminals shall be provided to
connect the power and control circuits (if applicable) to the light. The terminals shall be marked
A, B, C, and D. Terminal A shall connect to the +28 VDC circuit and terminal B shall connect
to ground (-28 VDC circuit). Terminal C is provided for remote de-energization and rearming of
the light if required.
3.13.3 Light turn-on feature. Provisions shall be incorporated so that upon removal of
the light from its mounting plate, the light will automatically energize in the ON position. This
may be accomplished either physically or electrically.
3.14 Batteries. The light shall be powered by four standard BA-30 cells conforming to
MIL-B-18. The batteries shall be arranged in series parallel, so as to provide a nominal open-
circuit voltage of 3 volts. The batteries shall be used only to provide power for the lamp and
under no conditions shall be used as a power source for any other component part of the light
such as a relay or other device. Unless otherwise specified (see 6.2), the batteries shall not be
furnished with the light.
3.15 Interchangeability. All parts having the same manufacturer's part number shall be
functionally and dimensionally interchangeable. The drawing number requirements of
ASME Y14.100, numbering, coding, and identification section, shall govern changes in the
manufacturer's part numbers.
3.16 Dimensions. The dimensions of the light shall remain within the envelope specified
in figure 1.
3.17 Weight. The weight of the light with lamp and batteries installed shall be not more
than 3.5 pounds.
3.18 Finishes and protective coatings.
3.18.1 Aluminum-alloy parts. Aluminum-alloy parts shall be covered with an anodic
film in accordance with MlL-A-8625, except as follows:
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