JLG sky trak mmv Service Manual page 498

Electrical System
With a Test Lamp
IMPORTANT: Only use the test lamp procedure on low
impedance power and ground circuits.
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 test lamp illuminates (full intensity), then the
circuit has good continuity.
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.
10.18
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 har-
ness 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
Relays are used to control a large amount of current by
using a small amount of control current flowing through
the relay coil.
1. Be sure the vehicle is on a level surface, the
implement grounded, parking brake engaged,
ignition switch is in the OFF position
2. Remove engine side battery box cover (1). Remove
wing nuts (2) and carriage bolts (3) and set cover
and mounting hardware aside for later re-assembly.
3. Disconnect the negative (-) battery cable (4) at the
battery negative (-) terminal on the battery in the
engine side battery box.
4. Disconnect the negative (-) cable (5) at the bottom of
the battery equalizer (6).
Model MMV Rev. 12-04