Shibaura ST330, Workshop Manual

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RELAY FOR HST BRAKE
SWITCH
Description
The relay fo r HST brak e switch is lo cated on
the steering colu mn in th e d ash board, and it
is connected with blue co lo r connecto r on
the HST circuit wire harn ess.
Relay is u sed to au to mat ically open a circuit.
A relay contain s two parts of a circu it. On e
part, th e control circuit, uses curren t to
energize a coil.
The other p art, the function circuit, is a
switch . When energized , th e coil of a relay
beco mes an electromagnet op ening o r
closing a sin gle circuit.
The HST brake switch relay u tilizes
single-pole, single-throw switches (SPST).
The function circu its are normall y close
when no current is being supp lied to the coil.
If a circu it with an SPST relay is energized
with current, the switch b ecomes open ed.
Relay Operation Testing
1. D isconn ect the neg ativ e (-) battery cable
from th e b attery.
2 . D isconnect and remove th e relay to b e
tested from the tractor.
3 . U s ing an oh mmeter, connect test p robes
to terminals "C" and "D " on the relay.
Observe the oh mmeter reading .
4 . T h ere should b e high resistan ce b etween
termin als "C" and "D", ind icating
continuity and that th e relay is
functioning prop erly when
non-energized. If there is no continuity,
th e relay is defective and needs
replaced.
5. To test the relay when energized, use
jumper wires to connect a 12-volt power
supp ly to terminals "A" and "B" (brass
terminals) on th e relay.
6 . To u ch ohmmeter test probes to t he "C"
and "D" terminals on the relay and
observe the ohmmeter. High resistance
between the terminals indicates that
th ere is no continuity and that th e relay
is fun ctioning properly. If th ere is
continuity between th e terminals, the
relay is defective and needs rep laced.
7. I n stall t he relay on to the tracto r.
8 . Con nect the negativ e (-) b attery cab le to
th e b attery.
547Y
548Y
549Y