MAINTENANCE OF M939 SERIES VEHICLES - OD1661 - LESSON 1/TASK 2
Once again he places the battery switch in the ON position and the
light switch to the SERVICE DRIVE position.
With the multimeter
negative lead connected to ground he connects the positive lead to
the circuit 16 wire (not to the terminal switch). The meter should
indicate battery voltage, which it does.
This indicates that the
headlamp beam selector switch is defective and needs to be replaced.
SGT Yowell replaces the headlamp beam selector switch in accordance
with the procedures contained in paragraph 4-39 of TM 9-2320-272-20-1.
Directional Signal System Troubleshooting.
In the following
paragraphs we will follow SGT Nertney as he troubleshoots the
directional signal system for the malfunction NO LIGHTS OPERATE WITH
DIRECTIONAL SIGNAL CONTROL LEVER IN ANY ON POSITION and reaches the
conclusion that the flasher is defective and needs to be replaced.
Prior to beginning the troubleshooting procedure, SGT Nertney first
reads DA Form 2404 and talks with the operator. After ensuring that
a malfunction exists, SGT Nertney reads through the troubleshooting
procedures to determine the necessary tools and special test
equipment required to perform this task.
For this particular
troubleshooting procedure, SGT Nertney will need a mechanic's general
toolbox and a multimeter. Once the necessary tools and special test
equipment have been gathered together, SGT Nertney configures the
vehicle according to the items listed in paragraph 3a(1) thru 3a(5)
on page 34 of this task.
At this point, SGT Nertney is ready to
begin the actual troubleshooting procedure.
The first step SGT Nertney will perform is to test the
control unit voltage feed. This is done by ensuring that the battery
switch is in the OFF position. Then he disconnects the control unit
harness connector from the directional signal control unit.
places the battery switch to the ON position and places the light
switch to the STOP TURN position. With the multimeter set to the 50
volt range, he connects the negative meter lead to the vehicle
chassis as a ground and the positive meter lead to the connector
terminal point G as shown in figure 23 (on the following page). The
meter should indicate battery voltage, which it did. Therefore, SGT