Craftsman 28906 Professional Shop Manual page 37

CRAFTSMAN
,
,
The voltage that shows-up on the meter is the
voltage that is being used to pass current
through a resistance in the circuit.
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 indicates a fairly
substantial problem that demands attention.
As an example, if the starter solenoid does not
engage properly, check for voltage drop between
the ground point for the starter solenoid and the
negative post on the battery. See Figure 7.48.
Figure 7.48
,
,
,
10.
With the starter engaged, this machine exhibited
a voltage-drop reading of 0.312 volts, indicating
a poor ground connection.
Individually, these readings should lead a techni-
cian to inspect the connection between the sole-
noid and the ground path on the first tractor (e.g.
mounting hardware, green wire with eyelet
beneath head of solenoid mounting bolt), or the
engine and the frame on the second tractor (e.g.
loose or rusty engine mounting bolts).
If both of these readings were found on the
same tractor, a common point in the system
would be the primary suspect (e.g. poor connec-
tion between negative battery cable and frame).
Applying this principle to the positive side of the
system. See Figure 7.50.
,
NOTE: With the starter engaged, this machine
exhibited a voltage-drop reading of 0.308 volts,
indicating a poor ground connection.
A similar ground-side test on a tractor with a
slow-cranking starter motor can be conducted
between the engine block and the negative bat-
tery post. See Figure 7.49.
Figure 7.49
11.
12.
13.
14.
15.
Figure 7.50
IMPORTANT: Ultimately, all positive current will
find its way from the positive post of the battery
to the negative post.
To check hot-side voltage drop: set-up a multi
meter to measure 12V DC.
Make a good electrical connection between the
red (+) probe and the positive post on the bat-
tery.
Make a good electrical connection between the
black (-) probe and the suspect point of the cir-
cuit.
Power-up the circuit in question.
The voltage that shows-up on the meter is the
power that is not following the intended path
back to the negative battery post.
34