stop start BMW M3 1992 E36 User Guide
Page 384 of 759
600-
4
ELECTRICAL
SYSTEM-GENERAL
Voltage
and
Voltage
Drops
The
wires,
connectors,
and
switches
that
carry
current
are
designed
with
very
low
resistance
so
that
current
flows
with
a
minimum
loss
of
voltage
.
A
voltage
drop
is
caused
by
higher
than
normal
resistance
in
a
circuit
.
This
additional
resistance
actually
decreases
or
stops
the
flow
of
current
.
A
voltage
drop
can
be
noticed
byproblems
ranging
fromdim
headlights
to
sluggish
wipers
.
Some
common
sources
of
voltage
drops
are
corroded
or
dirty
switches,
dirty
or
corroded
connections
or
contacts,
and
loose
or
corroded
ground
wires
and
ground
con-
nections
.
A
voltage
drop
test
is
a
good
test
to
make
if
current
is
flowing
through
the
circuit,
butthe
circuit
is
not
operating
correctly
.
A
voltage
drop
test
will
help
to
pinpoint
a
corroded
ground
strap
or
a
faulty
switch
.
Normally,
there
should
be
less
than
1
volt
drop
across
most
wires
or
closed
switches
.
A
voltage
drop
across
a
connector
or
short
cable
shouldnot
exceed
0
.5
volts
.
Voltage,
measuring
1
.
Connect
digital
multimeternegative
lead
to
a
reliable
ground
point
oncar
.
NOTE-
The
negative
(-)
battery
terminal
is
alwaysa
good
ground
point
.
2
.
Connect
digital
multimeter
positive
lead
to
point
incir-
cuit
you
wish
to
measure
.
See
Fig
.
1
.
If
a
reading
is
ob-
tained,
current
is
flowing
through
circuit
.
NOTE-
The
voltage
reading
shouldnot
deviate
more
than
1
volt
from
the
voltage
at
the
battery
.
If
the
voltage
drop
is
more
than
this,
check
for
acorroded
connector
or
cose
ground
wire
.
ELECTRICAL
TROLIBLESHOOTING
from
Battery
Fig
.
1
.
Digital
multimeterbeing
used
to
test
voltage
.
No
voltage
r_l
-1
Load
LJ
Switch
NOTE-
The
maximum
voltage
drop
in
an
automotive
circuit,
as
recommended
by
the
Society
of
AutomotiveEngineers
(SAE),
is
as
follows
:
0
voltsfor
small
vire
connections
;
0
.1
Volts
for
high
current
connections
;
0
.2
volts
for
high
current
cables
;
and
0
.3volts
for
switch
or
solenoidcon-
tacts
.
On
longer
wires
or
cables,
the
drop
may
be
slight-ly
higher
.
In
any
case,
a
voltage
drop
of
more
than
1.0volt
usually
indicates
a
problem
.
0013238
NOTE-
"
A
voltage
drop
test
is
generally
more
accuratethan
a
Voltage
drop,
testing
simple
resistance
check
because
the
resistances
in-
volvedare
often
too
small
to
measure
with
most
ohm-
Voltage
drop
can
only
be
checked
when
current
is
running
meters
.
For
example,
a
resistance
as
small
as0
.02
through
the
circuit,
suchasby
operating
the
starter
motor
or
ohms
would
results
in
a
3
volt
drop
in
a
typical
150
turning
onthe
headlights
.
A
digital
multimeter
should
beused
amp
starter
circuit
.
(150
amps
x
0
.02
ohms
=3
volts)
.
lo
ensure
accurate
readings
.
"
Keep
in
mind
that
voltage
with
the
key
on
and
voltage
with
the
engine
running
arenotthe
same
.
With
the
ig-
1
.
Connect
digital
multimeter
positive
lead
to
positive
(+)
nition
on
and
the
engine
off
(battery
voltage),
voltage
battery
terminalor
a
positive
power
supply
close
lo
bat
should
be
approximately
12
.6volts
.
With
the
engine
tery
source
.
running
(charging
voltage),
voltage
should
be
approx-
imately
14
.0
volts
.
Measure
voltage
at
the
battery
with
2
.
Connect
digital
multimeter
negativelead
to
other
end
of
the
ignition
on
and
then
with
the
engine
running
to
get
cable
orswitch
being
tested
.
See
Fig
.
2
.
exact
measurements
.
3
.
With
power
on
and
circuit
working,
meter
shows
volt-
age
drop
(difference
between
two
points)
.
This
value
should
not
exceed
1
volt
.
Page 682 of 759
67479
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43
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Page 688 of 759
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Exterior
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1994-96
(USA)
&
1997Except
318ti
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of
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Page 691 of 759
ELE-208
ELECTRICAL
WIRING
DIAGRAMS
88603
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Page 693 of 759
ELE-210
ELECTRICAL
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