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ELECTRICAL SYSTEM
10.
Applying this principle to the positive side of the
system. See Figure 7.43.
Figure 7.43
IMPORTANT: Ultimately, all positive current will
find its way from the positive post of the battery
to the negative post.
10a. To check hot-side voltage drop: set-up a
multi meter to measure 12V DC.
10b. Make a good electrical connection
between the red (+) probe and the positive
post on the battery.
10c. Make a good electrical connection between
the black (-) probe and the suspect point of
the circuit.
10d. Power-up the circuit in question.
10e. The voltage that shows-up on the meter is
the power that is not following the intended
path back to the negative battery post.
10f. Voltage drop on a good circuit should be
less than 0.1 volts. A voltage drop reading
on the meter of greater than 0.2 volts indi-
cates a fairly substantial problem that
demands attention.
•
As an example, if the tractor had a slow-turning
starter, the ground-side voltage drop measured
below 0.1 volts, and there was not a parasitic
load on the engine (e.g. PTO clutch that is not
fully disengaged), it would be logical for the tech-
nician to check voltage drop to the starter.
See Figure 7.44.
•
With the starter motor engaged, the voltage drop
reading here is nearly 0.6 volts, indicating a seri-
ous problem in the heavy-gauge circuit between
the starter and the battery.
10g. Checking voltage-drop at various points
along the circuit can help pin-point the
problem.
•
Check voltage-drop at the output lug on the
starter solenoid:
•
If there is a significant difference, the problem
lies between the lug on the solenoid and the lug
on the starter.
•
If there is little change, the problem lies further
up-stream.
•
Check voltage drop at the input lug on the sole-
noid. If there is significant difference between
the reading here and the reading at the output
lug (greater than 0.10 volt), then the contacts
inside the solenoid may be burned. If there is lit-
tle change, the problem lies further up-stream,
between the battery and the solenoid.
•
Results may be cross-checked by testing volt-
age drop across the two posts of the starter sole-
noid while cranking the starter motor.
138
Figure 7.44
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