John Deere stx38 - Manual (Page 146)

4 - 62
3/21/97
TESTS AND ADJUSTMENTS ELECTRICAL
TESTS AND ADJUSTMENTS
GROUND CIRCUIT TESTS
Reason:
To check for opens, loose terminal wire crimps, poor
connections, or corrosion in the ground circuit. The
voltmeter method checks ground connections under
load.
Equipment:
• Ohmmeter or voltmeter
W1—Frame Ground
W2—Engine Ground
Procedure:
OHMMETER METHOD:
1. Turn key switch to off position. Engage park brake.
2. Connect ohmmeter negative (black) lead to
negative terminal of battery. Put meter positive
(red) lead on negative terminal of battery and
record reading.
3. Put meter red lead on ground terminal of circuit or
component to be tested that is closest to the
battery negative terminal. Resistance reading
must be very close to or the same as the battery
negative terminal reading. Work backwards from
the battery on the ground side of the problem
circuit until the resistance reading increases above
0.1 ohms. The problem is between the last two test
points. If a problem is indicated, disconnect the
wiring harness connector to isolate the wire or
component and check resistance again. Maximum
allowable resistance in the circuit is 0.1 ohms.
Check both sides of connectors closely as
disconnecting and connecting may temporarily
solve problem.
VOLTMETER METHOD:
1. Put transmission in neutral. Engage park brake. Put
PTO switch in off position. Turn key switch to on
position.
2. Connect voltmeter negative (black) lead to negative
terminal of battery.
3. Put meter positive (red) lead on ground terminal of
component to be tested. Be sure the component
circuit is activated (key on, switches closed) so
voltage will be present at the component. Record
voltage. Voltage must be greater than 0 but less
than 1 volt. Some components will have a very
small voltage reading on the ground side and still
be operating correctly.
Results:
• If resistance is above 0.1 ohms, check for open
wiring, loose terminal wire crimps, poor
connections, or corrosion in the ground circuit.
• If voltage is 0, the component is open.
• If voltage is greater than 1 volt, the ground circuit is
bad. Check for open wiring, loose terminal wire
crimps, poor connections, or corrosion in the
ground circuit.
M55642
GROUND
M55950
GROUND