MG Magnette KA Instruction Manual page 112

Ammeter. T h e centre-zero ammeter which is incorporated i n t h e i n s t r u m e n t
panel indicates t h e actual c u r r e n t flowing i n t o o r o u t o f t h e battery. For instance,
suppose t w o amperes are consumed w h e n t h e side and tail-lamps are switched on,
t h e n i f t h e dynamo is generating at seven amperes t h e m e t e r w i l l show five amps.
o n t h e charge side o f t h e scale. This is t h e c u r r e n t i n excess o f t h e lamp and o t h e r
load which is available f o r battery charging purposes.
A
flickering o f t h e i n s t r u m e n t needle is caused by t h e p e t r o l pump, b u t should
cease w h e n t h e p u m p is switched o n and t h e engine is n o t r u n n i n g after t h e
p u m p has filled up. Shortage o f p e t r o l o r air leak o n t h e suction side w i l l
cause t h e p e t r o l p u m p t o keep o n operating.
Fuses. T h e separate fusing o f t h e various circuits ensures t h a t a s h o r t i n any
one does n o t affect t h e rest o f t h e electrical equipment.
It
w i l l be noticed t h a t
t h e fusing o f t h e lamps is such t h a t t h e r e is no risk o f t h e d r i v e r being plunged i n t o
t o t a l darkness. I f b o t h t h e headlamps, o r t h e side and tail-lamps, o r all t h e units
connected t o t h e auxiliary accessory t e r m i n a l fail t o function, examine t h e particular
fuse protecting them.
Remove t h e fuse f r o m its holder and see w h e t h e r t h e r e is a break i n t h e fuse
wire. Before replacing t h e fuse, inspect t h e units t h a t have failed, f o r evidence o f
s h o r t circuits o r o t h e r faults t h a t may have caused t h e fuse t o b l o w .
I f a fuse blows repeatedly and t h e cause cannot be traced, w e advise t h a t t h e
equipment is examined by a Lucas/Rotax Service Station.
The Cut-out. T h e function o f t h e cut-out is t o close t h e charging circuit
as t h e increased engine speed w h e n t h e car is starting causes t h e dynarno voltage
t o rise above t h a t o f t h e battery. W h e n t h e engine slows down, t h e dynamo voltaze
falls b e l o w t h a t o f t h e battery, and t h e reverse action takes place, i.e. t h e cut-out
opens and t h e r e b y prevents t h e battery f r o m discharging itself t h r o u g h t h e dynamo.
T h e question is sometimes asked w h e t h e r t h e operation o f t h e cut-out i n any
way depends upon t h e state o f charge o f t h e battery. There is n o such relation
between t h e t w o ; t h e sole function o f t h e c u t - o u t is t o switch o n t h e dynamo w i t h
rising engine speed and t o disconnect it w h e n t h e engine slows d o w n t o below a
certain speed. T h e cut-out is accurately set before leaving t h e W o r k s and does
n o t need any adjustment, and therefore t h e cover p r o t e c t i n g it is sealed.
Junction Box. This is f i t t e d w i t h a number o f glass barrel fuses, and holes
are provided i n t h e body o f t h e b o x t o carry spares. The fuses c o n t r o l t h e side and
tail-lamps, separate fuses f o r t h e headlamps, another fuse f o r auxiliaries such as
t h e h o r n and a f u r t h e r fuse marked
E,
which is f o r t h e dynamo field. T h e cut-out,
which is m o u n t e d o n t h e same base as t h e fuses, is provided w i t h a cover and under
n o r m a l circumstances need never be touched, its operations being entirely auto-
matic.
A
small circular junction b o x is placed beneath t h e fusebox and cut-out, w h i c h
forms a convenient connection p o i n t f o r wires t o t h e horn, off-side headlamp,
direction indicators and main battery positive pick-up. T h e scheme o f connections
i n this u n i t can be best understood by r e f e r r i n g t o t h e w i r i n g diagram.