Automatic Switches; Switch Wiring - Low Side, High Side - JLG E450A Service And Maintenance Manual

SECTION 7 - BASIC ELECTRICAL INFORMATION & ELECTRICAL SCHEMATICS
1. Remove prox switch from its mount.
2. Reconnect harness if it was disconnected for step a, and
turn on machine.
3. Hold switch away from metal and observe switch state
in the control system diagnostics using the Analyzer. See
vehicle or control system documentation on how to do
this.
4. Place sensing face of switch on the object to be sensed
by the switch. If that is not available, use a piece of fer-
rous metal physically similar to it. The switch state in the
control system diagnostics should change.
5. When reinstalling or replacing switch be sure to follow
mounting instructions and properly set the gap
between the switch and object sensed.

Automatic Switches

If the switch is actuated automatically, by temperature or pres-
sure for example, find a way to manually actuate the switch to
test it. Do this either by applying heat or pressure, for example,
to the switch. These switches may need to be energized to
actuate.
1. Connect instrumentation to monitor and/or control the
parameter the switch is measuring.
2. Observe switch state in control system with the Ana-
lyzer. See vehicle or control system documentation on
how to do this.
3. Operate system such that the switch actuates. This could
be going over a certain pressure or temperature, for
example. The state indicated in the control system
should change.

Switch Wiring - Low Side, High Side

When controlling a load, a switch can be wired between the
positive side of the power source and the load. This switch is
called a "high side" switch. The switch supplies the power to
the load. When a switch is wired between the negative side of
the power source and the load, it is a "low side" switch. The
switch provides the ground to the load.
A low side switch will allow voltage to be present on the load.
No power is applied because the switch is stopping current
flow. This voltage can be seen if the measurement is taken
with one test lead on the load and the other on the battery
negative side or grounded to the vehicle. What is actually
being measured is the voltage drop across the switch. This
could mislead a technician into thinking the load is receiving
power but not operating. To produce an accurate picture of
power or voltage applied to the load, measure voltage across
the load's power terminals. Also, the technician can measure
the voltage at both power terminals with respect to battery
ground. The difference between those two measurements is
the voltage applied to the load.
7-4
7.4 APPLYING SILICONE DIELECTRIC COMPOUND TO
ELECTRICAL CONNECTIONS
NOTE: This section is not applicable for battery terminals.
JLG PN 0100048 DIELECTRIC GREASE (NOVAGARD G661) IS THE ONLY MATE-
RIAL APPROVED FOR USE AS A DIELECTRIC GREASE.
NOTE: Do NOT apply dielectric grease to the following connec-
tions:
• Main Boom Rotary sensor connections (on Celesco Sensor),
• LSS Modules connections,
• Deutz EMR 2 ECM connection.
Silicone Dielectric Compound must be used on all electrical
connections except for those mentioned above for the follow-
ing reasons:
• To prevent oxidation at the mechanical joint between male
and female pins.
• To prevent electrical malfunction caused by low level con-
ductivity between pins when wet.
Use the following procedure to apply Silicone Dielectric Com-
pound to the electrical connectors. This procedure applies to
all plug connections not enclosed in a box. Silicone grease
should not be applied to connectors with external seals.
1. To prevent oxidation, silicone grease must be packed
completely around male and female pins on the inside
of the connector prior to assembly. This is most easily
achieved by using a syringe.
NOTE: Over a period of time, oxidation increases electrical resis-
tance at the connection, eventually causing circuit failure.
2. To prevent shorting, silicone grease must be packed
around each wire where they enter the outside of the
connector housing. Also, silicone grease must be
applied at the joint where the male and female connec-
tors come together. Any other joints (around strain
reliefs, etc.) where water could enter the connector
should also be sealed.
THIS CONDITION IS ESPECIALLY COMMON WHEN MACHINES ARE PRESSURE
WASHED SINCE THE WASHING SOLUTION IS MUCH MORE CONDUCTIVE THAN
WATER.
3. Anderson connectors for the battery boxes and battery
chargers should have silicone grease applied to the con-
tacts only.
3121714