Ignition Switch; Solenoids And Relays - Stiga MPV 320W Workshop Manual

WORKSHOP MANUAL
MPV 320W / 520W

7.2.4 Ignition switch

NOTE - Refer to the wiring diagram of the machine (continuity diagram) to determine switch func-
tions and test using the methods described.
The ignition switch incorporates a number of functions. It is a three-position switch: OFF, RUN,
START with momentary contact.
Use an ohmmeter to check for continuity in each position.
• «OFF» Position - There must be no continuity between contacts.
• «RUN» Position - There must be continuity between contacts 30 and 15/54.
• «START» Position - Hold the switch in the START position while testing. There must be conti-
nuity between contacts 30, 15/54 and 50. These connections apply power to close the solenoid
contacts and engage the starter motor.
In addition to the tests above, set the switch to the «RUN» position and check between each con-
tact and the ground (metal part) to ensure that no terminals are grounded. If the switch is function-
ing properly, there will be no continuity between the contacts other than that described.

7.2.5 Solenoids and Relays

Solenoids and relays are both magnetically operated devices. Both devices operate on the prin-
ciple that passing a current of electricity through a coil of wire will create a magnetic field strong
enough to attract a piece of iron or steel. Each device uses this principle in a slightly different man-
ner.
• Solenoids - A basic solenoid consists of a coil of wire wound around a hollow tube. A magnetic
core slides inside the tube. When current is passed through the coil, the core is pulled into the
solenoid with considerable force. With proper design, a solenoid can exert considerable force
over a distance of several inches. A solenoid can therefore, pull a lever, close a heavy contact,
or perform other jobs that require a straight line pull.
• Relay - A basic relay consists of a coil of wire wound around a soft iron (magnetic) core. When
current is passed through the coil, the core is magnetized and pulls down on a magnetic lever.
The lever in turn is attached to several switch contacts which open or close other electrical cir-
cuits. In this fashion, a small current can control one or more larger electrical currents and actu-
ate several other devices. In most cases a relay contact moves only a fraction of an inch and the
magnetic pull is low.
If a relay or solenoid fails to operate the cause may be either electrical or mechanical.
To check electrically, connect a voltmeter across the coil of the device and activate the circuit that
operates the relay or solenoid. If the meter indicates no voltage is applied, the cause lies in the
control circuit.
Chapter
7 - ELECTRICAL SYSTEM
EDITION PAGE
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