accordance with Federal Motor Carrier Safety Regulation 393.77. The heater shall have a rated
capacity of not less than 25,000 Btu per hour. The heater shall be connected to the engine
coolant system and shall be provided with not less than a 6-gallon per minute (gpm) capacity
circulating pump. The heater shall be capable of maintaining the temperature inside the vehicle
at a minimum of 70F midway between the floor and the ceiling in an ambient air temperature of
0F, with no passengers. Controls for operating the heater shall be located in the driver's area
and shall be identified as to purpose and position (on-off).
3.5.6 Warning light. Unless two warning lights are specified (see 3.5.7), a single rotating
warning light, conforming to MS51317, shall be installed with reinforcement at the point of
attachment, on the vehicle centerline where 360-degree visibility is provided. The warning light
shall be operated by means of a separate switch with a red indicator light located on the
instrument panel and marked to indicate the function of the switch. Unless otherwise specified
(see 6.2), the color of the warning light shall be red. At the option of the manufacturer or when
specified (see 6.2), the light shall be removed for shipment of the vehicle. When removed, the
light shall be stowed within the vehicle and the roof opening shall be provided with a
weatherproof cover. Provisions for reinstalling the light, including access to the light wiring and
mounting devices from inside the vehicle, shall be provided.
3.5.7 Warning lights. When specified (see 6.2), two rotating warning lights shall be
installed, with reinforcements at the point of attachment. The lights shall be mounted on the
forward portion of the vehicle roof, one on the streetside and one on the curbside, in a position
affording 360-degree visibility. The revolving light base shall be 4 to 5 inches high. Each light
shall have a clear dome, and shall have four high intensity, sealed beam lamps, each having a
minimum of 35,000 candle power. Unless otherwise specified (see 6.2), two of the lamps shall
be white and two shall be red, installed in alternating colors. The lights shall flash across a
viewer's line of vision at a minimum flash rate of 80 flashes per minute. The two warning lights
shall be operated by means of one separate heavy duty switch. The switch shall be located on the
instrument panel, so positioned as to be readily accessible to the driver, and shall be marked to
indicate the function of the switch. A red indicator light shall be provided. At the option of the
manufacturer or when specified (see 6.2), the lights shall be removed for shipment of the vehicle.
When removed, the lights shall be stowed in the vehicle and the roof openings shall be provided
with weatherproof covers. Provisions for reinstalling the lights, including access to the light
wiring and mounting devices from inside the vehicle, shall be provided.