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6.10.2 Checking for voltage presence
Check for voltage presence if the circuit does not functions. Connect one of the tester
wires to the battery negative pole of the reliable earthing of the tractor. Connect the other
tester wire to the terminal of the circuit electric terminal, preferably to the closest to AB or
fuse. If the test lamp lights up on the tester, then there is voltage in this circuit section and
this confirms operability of the circuit between this terminal and AB. While working in the
same manner test the remaining part of the circuit. If voltage is absent, this is evidence of
malfunction between this circuit point and the previously tested point (where voltage was
present). In the most cases, the reason is electric connections loosening and degradation
of contacts quality. Keep in mind, that some of the circuits of the vehicle-mounted electric
equipment receive power supply only when the starter and instruments switch is in position
I (instruments are ON) or II (starter is ON (not fixed position)).
6.10.3 Searching for short-circuits
One of the methods for short-circuits searching is to remove the fuse and connecting
the test lamp or voltmeter instead of it. There should be no voltage in the circuit. Jerk the
wiring and monitor the test lamp indications. If lamp starts blinking, then there is ground
fault somewhere in this circuit, which could be caused by the wire insulation wearing. The
same test can be performed for each circuit component, including the switch of this circuit.
6.10.4 Checking for electric element earthing presence
This test is performed to determine availability of reliable earthing of the electric ele-
ment. Deactivate the AB earthing switch and connect one of the wires of the test lamp with
stand-alone power supply source to certainly reliable earthing. Connect the other lamp
wire to the harness or terminal to be tested. If the lamp lights up, then the earthing is nor-
mal (and vice versa). Meanwhile, if minus power supply circuit of the high current consum-
er is tested, then it is necessary to use the tester lamp of power at least 21 W. In case of
poor earthing contact, the high current consumer will not work and low-power lamp will
light up.
6.10.5 Checking for electric circuit discontinuation
This test is performed to find discontinuations in the electric circuit. When the circuit
power supply is turned off, test it using the test lamp, which is equipped with the stand-
alone power supply source. Connect the tester wires to both ends of the circuit (or to
"power" end (+) and to the tractor reliable earthing). If the test lamp lights up, then there is
no discontinuation in the circuit. If the lamp does not lights up, then this is evidence of cir-
cuit discontinuation. In the same manner, it is possible to check operability of the switch by
connecting the tester to its terminals. When the switch is moved into position "ON", the test
lamp should light up. Meanwhile, if switch, transmitting power to the high current consumer
is tested, then it is necessary to use the tester lamp of power at least 21 W. In case of the
switch poor contacts the high current consumer will not work and low-power lamp will light
up.
6.10.6 Discontinuation isolation
While performing diagnosis of the circuit with suspected discontinuation it is difficult
to visually determine the reason of the malfunction, since visual inspection of terminals for
corrosion or insufficient quality of their contacts is hindered because of restricted access to
them (usually terminals are covered by the connector housing). In many cases, continua-
tion can be restored by sharp jerking of the connector housing on the sensor or by its wire
harness. Keep this in mind while trying to isolate the malfunction reason in the circuit with
suspected discontinuation. Irregular malfunctions can be caused by terminals corrosion or
poor contacts.
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921.6-0000010 OM
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