ELECTRICAL
EQUIPMENT
(ii)
Adjustment
Adjustment of the horn does not
alter the pitch of the note, but
takes up wear of the moving parts
which
if
uncorrected, would re-
sult in loss of power and rough-
ness of tone.
The horn must not be used re-
peatedly when out of adjustment,
as the resulting excessive current
may damage it. The maximum
current consumption of a horn in
correct adjustment is
64 amps.
for WT614 horns and 8 amps. for
WT618 horns (the total current,
taken by both horns together,
will naturally be twice the figure
quoted).
If it is desired to check the current
consumption of the horns, break
the circuit at some convenient
point and connect an ammeter,
0-30
or
0-50
amps., in series
with the horns.
If the consumption is in excess of
13
amps. for WT614 horns or
16 amps. for WT618 horns, it will
be necessary to adjust the horns,
even if they are apparently oper-
ating correctly. Horns will norm-
ally
be tested with the car sta-
tionary and the battery at roughly
its nominal voltage, but under
running conditions with the bat-
tery charging the voltage may be
appreciably higher, and may over-
load the horns if the latter are not
in correct adjustment.
If the horns are badly out of
adjustment, it will be necessary to
short circuit the horn
fuse,Al-A2,
as otherwise the excessive current
taken by the horns during the
process of adjustment might re-
sult in its repeated blowing.
Withdraw the cover securing
screws and remove the covers.
Disconnect the supply lead from
one horn, taking care that it cannot
touch any .part of the car and so
cause a short circuit.
Horns must always be securely
bolted down when carrying out an
adjustment, and
if
it is necessary
to remove a horn from the car for
testing, it must always be firmly
clamped by its securing bracket
for the test or adjustment to be
effective.
Slacken the
locking nut on the
fixed contact and rotate the ad-
justing nut in a clockwise direc-
tion until the contacts are just
separated, as indicated by the
horn failing to sound. Turn the
adjusting nut
half
a
turn
in the
opposite direction, and hold it
while tightening down the
locking
nut. Check the current consurnp-
tion of the horn,
if
the current is
incorrect, make further very fine
adjustments to the contact break-
er, turning the adjusting screw in
a clockwise direction in order to
decrease the current, and
vice
versa.
Adjust the other horn
in
a similar
manner.
(b)
Internal Faults
If the note cannot be improved by
adjustment of the contact breaker,
examine the movement for the follow-
ing faults
:
(i)
Contacts badly worn,
so that
correct adjustment is impossible.
A new set of contacts,
i.e.,
moving
contact and spring, and fixed
contact and adjusting screw, must
be fitted, and the horn adjusted
as described above.
(ii)
Faulty resistance.
To prevent
excessive sparking as the horn
contacts separate, a carbon resist-
ance is connected across the horn
coil. The correct resistance valve
is 8 ohms. On model
WT618
horns the contact breaker ter-
minal block is manufactured from
a resistance material and this
serves as the spark suppressing
resistance.
If
the resistance be-
comes open circuited the horn
note will become rough and fierce
sparking
will
occur as the horn
contacts separate.
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