Automatic Switches; Switch Wiring - Low Side, High Side - JLG 1932RS/6RS Service And Maintenance Manual

Automatic Switches

If the switch is actuated automatically, by temperature or pressure 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 Analyzer. 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.
3121273
SECTION 7 - GENERAL ELECTRICAL INFORMATION & SCHEMATICS
7-13