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 432 of 759
612-4
SWITCHES
AND
ELECTRICAL
ACCESSORIES
Fig
.
6
.
Ignition
switch
set
screws
(arrows)
.
Ignition
lock
cylinder,
replacing
NOTE-
On
cars
with
EWS
11(production
date
1/95
and
later),
the
ring
antenna
surrounding
the
ignition
switch
must
be
removed
.
See
515
Central
Locking
and
Anti-theft
.
1
.
Insert
master
key
finto
lock
cylinder
and
turn
60°
to
"ra-
dio"
position
.
See
Fig
.
7
.
Fig
.
7
.
Turn
ignition
switch
60°
to
"radio"
position
(arrow)
.
2
.
Insert
a
thin
piece
of
stiff
wire
into
opening
in
lock
cylin-
der
and
pull
lockcylinder
out
.
See
Fig
.
8
.
NOTE-
On
early
cars
(up
to
production
date
1ol95),
turn
lock
cylinder
back
12°
to
release
.
INTERIOR
SWITCHES
0012555
0011807
0011808
Fig
.
8
.
With
ignition
key
in
"radio"position,
insert
stiff
wire
into
lock
opening
to
release
cylinder
.
Headlight
and
Foglight
Switch
Assembly
The
headlight
and
foglight
switches
are
retained
in
the
left
dashboard
insert
.
This
alsocontains
the
driver's
side
face
lev-
e¡
air
vents
.
To
service
either
switch,
remove
insert
byremov-
ing
a
single
screw
.
See
Fig
.
9
.
NOTE-
Access
to
electrical
hamess
connectors
behind
dash
insert
may
be
easier
if
lower
left
dash
trim
and
driverside
knee
bolsterare
removed
.
See
513
Interior
Trim
.
Fig
.
9
.
Remove
retaíning
screw
to
pull
out
left
dash
insert
(arrow)
.
Page 478 of 759
721-2
AIRBAG
SYSTEM
(SRS)
Fig
.
1
.
Airbag
system
components
.
AIRBAG
SENSORSAND
ELECTRONICS
CA
UTION-
"
If
an
airbag
is
activated,
the
following
compo-
nents
must
be
replaced
:
Airbag
with
contact
ring
;
-Pyrotechnic
seat
belt
tensioners
(if
fitted)
;
-SRS
Control
module
;
-Impact
sensors
;
All
airbags
which
did
not
deploy
.
"
Consult
your
BMW
dealer
for
parts
and
service
information
.
TheE36
airbag
system
consists
of
the
following
compo-
nents
:
crash
sensors
(in
earlycars,
through
1993),
an
elec-
tronic
control/monitoring
module
(with
integrated
crash
sensor
in
ZAE
systems),
an
indicator
light
in
the
instrument
panel,
and
inflatable
airbags
equipped
with
gas
generators
in
the
steering
wheel
and
in
the
passenger
side
of
the
instrument
panel
(ZAE
systems)
.
Some
1997
and
al¡
1998
carsalso
have
side-impact
airbags
in
the
front
doors
.
AIRBAG
SENSORS
AND
ELECTRONICS
1.
Crash
sensors
(through
1993)
wheel
2
.
SRS
control
module
in
front
of
5
.
Side-impact
airbags
(1997/98)
glove
compartment
(through
6
.
ZAE
control
module
under
rear
1993)
seat
(from
1994)
3
.
Passenger
side
airbag
unit
in
7
.
Side-impact
airbag
crash
sensors
dashboard
(ZAE
system)
in
door
silis
(1997/98)
4
.
Driver
side
airbag
unitin
steering
8
.
Knee
bolsters
In
addition
to
the
airbags,
the
vehicles
are
equipped
wíth
knee
bolsters
for
extra
protection
.
SRS
Warning
Light
and
Fault
Display
The
airbag
system
utilizes
a
self-diagnostic
control
module
to
detect
and
store
system
faults
.
If
a
fault
is
detected,
the
SRS
indicator
in
the
instrument
cluster
comes
on
and
stays
on
.
When
the
ignition
key
is
tumed
on,
the
indicator
light
will
illu-
minate
for
approximately
4-6
seconds
.
The
illuminated
light
indicates
the
self-testof
the
electronic
control/monitoring
module,
the
ignítors
and
crash-sensorcircuits,
and
the
system
wiring
.
The
airbag
system
should
be
inspected
byan
autho-
rized
BMW
dealer
if
the
indicator
light
does
not
come
on,
ifit
does
not
go
out
in
approximately
4-6
seconds
after
switching
onthe
ignition,
or
if
the
light
comes
on
during
driving
.
If
the
system
has
detected
a
fault,
the
light
will
come
on
and
stay
on
.