TM-9-2350-311-34-2
CAB, ARMAMENT, SIGHTING AND FIRE CONTROL, ELEVATING AND TRAVERSING SYSTEMS AND ASSOCIATED COMPONENTS HOWITZER, MEDIUM, SELF-PROPELLED, 155MM
TECHNICAL MANUAL; DIRECT AND GENERAL SUPPORT MAINTENANCE MANUAL
SEPTEMBER 1994
TM-9-2350-311-34-2 - Page 39 of 552
TM 9-2350-311-34-2
1-14.4 Location and Description of Overall Cab Electrical System
The cab uses a 28 volt DC electrical system with power furnished from the hull. Electrical contact is made with bus bars
fastened to a 1/5th segment of the hull race ring. Power reaches the cab through whichever one of the five contact arm
assemblies (1) happens to be in contact with the bus bars on the hull. Three intercom lines and two telephone lines go
directly to amplifier AM1780/VRC (2). The cab power line comes into the power relay box assembly (3) and power is distrib-
uted through the following circuits:
a. Wire 100 provides main cab power. Its connection to the gunner’s selector switch box assembly (4) allows ON/OFF
control of all power to the cab, MAN UAUPOWER control of traverse, elevation control, and lighting of circuits. Wire 100
also provides power to the nuclear, biological, and chemical (NBC) protection system in M109A4/M109A5 howitzers.
b. Wire 148 provides power to amplifier AM1780/VRC (2).
c. Wire 645 provides power to pressure switch (5) for control of power pack assembly (6) direct current motor (7).
d. Wire 104 provides power to power pack assembly (6) direct current motor (7).
e. Wire 141, 142, 143, L1, and L2 support intercommunication/telephone circuits.
LEGEND:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
Contact arm assembly (5)
Amplifier AM1780/VRC
Power relay box assembly
Gunner’s selector switch box assembly
Pressure switch
Power pack assembly
Direct current motor
Intercom control box C2298/VRC (2)
Elevation selector valve assembly
Assistant gunner’s control handle
11.
12.
13.
14.
15.
16.
17.
18.
19.
M15 elevation quadrant
M117/M117A2 panoramic telescope
M118A2/M118A3 elbow telescope
Traverse mechanism bypass valve assembly
Clutch valve solenoid
Dome light assemblies (3)
NBC M3 electrical air heater (4)
M2A2 air purifier
NBC control box assembly
1-19
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