MAINTENANCE OF M939 SERIES VEHICLES - OD1661 - LESSON 1/TASK 2
together, SGT Yowell configures the vehicle according to the list of
items contained in paragraphs 3a(1) thru 3a(5) on page 34 of this
task. Now SGT Yowell is ready to begin troubleshooting.
In this step, SGT Yowell tests the headlamp connector
voltages for both sides. To accomplish this, SGT Yowell ensures that
the battery switch is in the OFF position.
He then disconnects
circuits 18 and 91 at the headlights. After circuits 18 and 91 have
been disconnected, SGT Yowell places the battery switch to the ON
He then places the lighting switch to the SERVICE DRIVE
position, and presses the dimmer switch to LOW BEAM.
multimeter set to the 50 volt range, SGT Yowell connects the positive
lead of the multimeter to the wire from circuit 18 and the negative
lead to the wire from circuit 91. The meter should indicate battery
voltage, which it did, so SGT Yowell visually inspects the headlamp
body pin connector for corrosion and loose connections.
the connections are tight and there is no evidence of corrosion, SGT
Yowell will proceed with the troubleshooting procedures.
In this step, SGT Yowell will test the headlamp beam
He places the battery switch and the light switch
in the OFF positions. He then disconnects the wires from circuit 17
and 18 at the beam selector switch. With the multimeter set to the
50 volt range, SGT Yowell places the battery switch and the light
switch to the ON positions.
SGT Yowell then connects the positive
meter lead to terminal 17 on the switch and the negative meter lead
to the vehicle chassis as a ground. At this point SGT Yowell makes a
note of the meter reading. He then connects the positive meter lead
to the exposed terminal 18 on the switch and leaves the negative lead
connected as before.
He once again makes a note of the meter
Since battery voltage was not indicated at either terminal (17 and
18), SGT Yowell operates the headlamp beam selector switch several
Since battery voltage is still not indicated, SGT Yowell places the
battery and the light switches to the OFF position.
disconnects the circuit 16 wire from the beam selector switch.