Lull 944E-42 Service Manual - Manual (Page 210)

Electrical System
9-52 944E-42
Testing for Short to Ground
The following procedures test for a short to ground in a
circuit.
With a DMM
1. Remove the power feed (i.e. fuse, control module)
from the suspect circuit.
2. Disconnect the load.
3. Set the rotary dial of the DMM to the Ohm position.
4. Connect one lead of the DMM to one end of the
circuit to be tested.
5. Connect the other lead of the DMM to a good
ground.
6. If the DMM does NOT display infinite resistance
(OL), there is a short to ground in the circuit.
With a Test Lamp
1. Remove the power feed (i.e. fuse, control module)
from the suspect circuit.
2. Disconnect the load.
3. Connect one lead of the test lamp to one end of the
circuit to be tested.
4. Connect the other lead of the test lamp to battery
positive voltage.
5. Connect the other end of the circuit to ground.
6. If the lamp illuminates (full intensity), then the circuit
has good continuity.
Testing a Fuse Powering Several Loads
1. Review the system schematic and locate the fuse
that is open.
2. Open the first connector or switch leading from the
fuse to each load.
3. Connect a DMM across the fuse terminals (be sure
that the fuse is powered).
• When the DMM displays voltage the short is in
the wiring leading to the first connector or switch.
• If the DMM does not display voltage, refer to next
step.
4. Close each connector or switch until the DMM or
analog tester displays voltage in order to find which
circuit is shorted.
Testing for Electrical Intermittence
Perform the following procedure while wiggling the
harness from side to side. If possible, continue this at
6-inch intervals while watching the test equipment.
• Testing for Short to Ground
• Testing for Continuity
Testing Relays from the Fuse Block
Relays are used to control a large amount of current by
using a small amount of control current flowing through
the relay coil.
1. Park the machine on a firm, level surface, level the
machine, fully retract the boom, lower the boom,
place the transmission control lever in
(N) NEUTRAL, engage the park brake and shut the
engine OFF.
2. Place a Do Not Operate Tag on both the ignition key
switch and the steering wheel, stating that the
machine should not be operated.
3. Open the engine cover. Allow the system fluids to
cool.
4. Properly disconnect the batteries.
5. Remove the cover plate from the right side console
(7).
6. Refer to the relay location chart, on page 9.4, for the
location of the relays within the fuse block.
7. Remove the suspect relay from the machine.
MU7590
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