82.3-0000010 OM
235
6.12.2 Check for voltage
Check for voltage shall be carried out in case of circuit malfunctioning. Connect one
of the tester wires either to the negative battery terminal or to the tractor safe “ground”.
The other tester wire shall be connected to the terminal of the circuit electrical connection,
preferably the one located nearer to the AB or the fuse. If the pilot lamp on the tester lights
up, there is voltage on this circuit segment which proves circuit operability between this
terminal and the AB. Acting analogically, inspect the rest part of the circuit. Detecting ab-
sence of voltage supply points at the failure between this circuit point and the last of those
checked before (where voltage supply was detected). In most cases, the reason for mal-
functioning is weakening of electrical connections and contact quality disturbance. Re-
member that voltage is supplied to some of the on-board electrical equipment circuits only
in the positions of the starter and instrument switch “I” (instruments ON) or “II” (starter ON
(non-fixed position)).
6.12.3 Search for short circuit
One of the short circuit search methods is removal of the fuse and connection of a
continuity test lamp or a voltmeter instead of it. There shall be no voltage in the circuit.
Shake the wire looking at the test-lamp. If the lamp starts blinking, then there is a ground
failure in this cable, possibly caused by wear of wire insulation. A similar check can be car-
ried out for each of the circuit elements including the cutout switch of this circuit.
6.12.4 Check of availability of the electrical element “ground”
This check is carried out with the purpose of determining the availability of the elec-
trical element’s safe “ground”. Disconnect the AB by means of the “ground” disconnect
switch and connect one of the wires of the continuity test lamp, equipped with the self-
contained power supply, to the safe “ground”. The other wire of the tester shall be con-
nected to the cable or terminal which is being checked. If the lamp lights up, then ground-
ing is ok (and vice versa). If the minus supply circuit of the high-current load is under
checking, it is required to use the continuity test lamp with the capacity of not less than 21
W because with a bad contact of the “ground”, the high-current load will not operate and
the lamp of a small capacity will light.
6.12.5 Check of electrical circuit breakage
This check is carried out with the purpose of detecting electrical circuit breakages.
After disconnection of the circuit power supply, check the circuit by means of a continuity
test lamp equipped with a self-contained battery. Connect the continuity test lamp wires to
both sides of the circuit (or to the high-power end (+) and to the reliable tractor “ground”), if
the control lamp lights up it means the circuit has no breakage. The lamp’s failure to light
up indicates that the circuit has conductivity fault. The operability of the switch can be
checked in a similar way by connecting the continuity test lamp to its terminals. While shift-
ing the switch into the position “On”, the test lamp shall light up. If the switch commutating
power supply for a high-current load is under check, it is also required to use the continuity
test lamp with a power of not less than 21 W. The reason is that with the bad contact in the
switch, a high-current load will not operate and the lamp with small power will light.
6.12.6 Locating circuit break
While carrying out diagnostics of the circuit segment suspected of breakage, it is dif-
ficult to detect circuit breakage visually as inspection of terminals for presence of corrosion
or defects in their contact quality can be difficult due to limited access to them (as a rule
terminals are covered with the connection housing). Abrupt shaking of the connection
housing on the sensor or of the bundled cable leads to conductivity recovery in many cas-
es. Remember this when trying to localize the reason for a failure of the circuit suspected
of breakage. Occasionally arising failures can be caused by terminals oxidation or defects
in contact quality.
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