1994 BMW 325i electrical

The
left
latch
in
the
fully
automatic
version
hastwo
mi-
croswitches
(S7
and
S8)which
signal
open,
closed
and
latched
states
.
See
Fig
.
8
.

The
length
of
the
dead
center
point
rod
is
critica¡
lo
correct
opening
and
latching
of
the
convertible
top
.
See
Fig
.
9
.

Dead
Center
Point
Rod

"
Dimension
A
........
205
.5
f
1
mm
(8
.09
t0
.04
in)

Visor
Latch
Motor

The
fully
automatic
convertible
top
is
latched
and
unlatched
by
one
electric
motor
installed
in
the
front
roof
bow
.
To
re-
place,
remove
front
cover
trim
from
the
roof
.
Remove
electri-
cal
harness
connectors
from
motor,
andremove
mounting
screws
.
Slide
the
motor
off
the
output
shafts
to
the
left
and
right
latches
.

During
reinstallation,
theoutput
shafts
must
be
tumed
until
the
S8
microswitch
in
the
left
latch
is
tripped
.

Convertible
top
and
frame,
replacing

1
.
Open
convertible
top
partially
.
Open
convertible
top
lid
.



Fig
.
9
.



Preset
lengthof
dead
centerpoint
rod
.
Open
back
windows
.

2
.
Fully
automatic
power
convertible
top
:
Remove
front
cover
trim
from
top
.
Disconnect
electrical
harness
con-

nectors
from
frontlatch
motor
.
Disconnect
connectors

from
S7
and
S8
microswitches
at
left
latch
.

Motors
M1
Convertible
top
M2
Convertible
top
lid
M3Front
latch
(fully
automatic
top)

Microswitches
S1
&S2
In
convertible
top
motor
S3
In
convertible
top
storage
compartment
S4
In
top
linkage
(semi-automatic
only)
S5
In
luggage
compartment
latch
S6
In
right
convertible
top
lid
latch
S7&S8
In
left
conv
.
top
latch
(fully
automatic)

Fig
.
8
.



Locationof
automatic
and
semi-automatic
convertible
latch
mechanisms,
motors
and
microswitches
.

CONVERTIBLE
TOP



541-5

POWER
CONVERTIBLE
TOP

541-
6



CONVERTIBLE
TOP

3
.
Remove
headliner,
starting
from
front
and
working



7
.
Remove
fasteners
in
bottom
of
storage
compartments

backward
.
Note
arrangement
and
lacing
of
tensioning



behind
door
posts
and
lift
out
complete
top
.
Note
num

cable
so
it
can
be
reinstalled
in
its
original
configura-



ber
of
shims
on
horizontal
mounting
bolt
.
See
Fig
.
12
.

tion
.
See
Fig
.
10
.

0012748

Fig
.
10
.
Headliner
tensioning
cable
and
some
of
its
retaining
eyelets
(arrows)
.

4
.
Disconnect
electrical
harness
connector
from
S4
mi-

croswitch
in
middle
linkage
of
convertible
top
.

5
.
Disconnect
electric
motor
linkage
rods
in
convertible

top
storage
compartment
behind
left
rearseat
.
See
Fig
.

Vizib1

Fig
.
11
.
Convertible
top
linkage
rods(arrows)
in
compartment
behind
left
rear
seat
.

POWER
CONVERTIBLE
TOP

8
.
Installation
is
reverse
of
removal
.
Be
sure
to
replace
U-

shaped
shims
on
horizontal
mounting
bolts
.
See
Fig
.

13
.

0012754

Fig
.
13
.
Horizontalpositioning
bolt
(A)
and
U-shaped
adjusting
shims
(B)
for
convertible
top
.
One
of
two
main
mounting
nuts
(ar-
rows)
also
visible
.

6
.
Pull
electrical
harness
through
to
disengage
from
top
.



9
.
To
adjust
position
and
fit
oftop,
Rmove
or
add
U-
shaped
shims
until
top
is
properly
aligned
.
Tighten
nuts

and
screws
.

Convertible
top
drive
motor,
replacing



5
.
Working
in
convertible
top
storage
compartment
be-
hind
driver's
seat,
remove
convertible
top
linkage
rods
1
.
Open
convertible
top
partially,
stopping
when
convert-



from
top
of
motor
.
Refer
to
Fig
.
11
.
ible
top
lid
is
fully
upen
.
Remove
lid
.

2
.
Release
luggage
compartment
lock-out
by
pressing
on
microswitch
in
right
convertible
top
lid
latch
.
See
Fig
.

14
.

0012745

Fig
.
14
.
Rightside
convertible
top
lid
latch
.
Arrow
points
to
location
of
luggage
compartment
lock-out
microswitch
.

3
.
Open
luggage
compartment
.
Remove
trim
and
inner

lining
from
left
side
of
compartment
.

4
.
Disconnect
electrical
harness
connectors
at
top
motor
.

Release
emergency
release
cable
from
lever
.
Push
le-

ver
up
to
release
motor
.
See
Fig
.
15
.

uu12759

Fig
.
15
.
Convertible
top
motor
(A)
and
release
lever
(B)
in
luggage

compartment
.

CONVERTIBLE
TOP



541-
7

6
.
Remove
four
fastenersholding
motor
to
body
and
re-

move
motor
through
luggage
compartment
.
See
Fig
.

16
.

0012761

Fig
.
16
.
Convertible
top
motor
mountingscrews
(arrows)
.
Gasket
(A)
mustbe
renewed
when
motor
is
replaced
.

7
.
Installation
is
reverse
of
removal
.
Keep
the
following
in

mind
:

"
Replace
sealing
gasket
between
top
of
motor
and

body
.

"
Securemotormountingscrews
with
Locktite
®
270
or
equivalent
.

Tightening
Torque

"
Convertible
top
motor
to
body

mountingscrews
...
...
.
.
.........
10
Nm
(7
.5
ft-Ib)

Convertible
Top
Emergency
Operation

A
malfunction
in
the
electrical
system
or
another
fault
in
the

convertible
top
mechanism
can
cause
the
automatic
or
semi-
automatic
top
to
be
stuck
in
open,
shut,
or
intermediate
posi-

tion
.
The
following
general
procedures
are
suggested
in
order

to
close
the
top
in
an
emergency
situation
.
Resetting
proce-

dures
for
convertible
top
synchronization
after
emergency
clo-

sure
are
beyond
the
scope
of
this
manual
.

Main
Motor
.
To
release
thetop
linkage
from
the
motor,
lift

the
left
comer
of
the
rearseat
to
access
emergency
release

handle
.
See
Fig
.
17
.

POWER
CONVERTIBLE
TOP

600
Electrical
System-General

GENERAL
.
...........
.
.
.
.
.
.
.
.
.
...
.
...
600-1

Voltage
and
Polarity
........
.
.
.
.
.
.
.
.....
600-1

Ming,
Fuses
and
Relays
............
.
.
.
.
600-1

Electrical
System
Safety
Precautions
...
.
.
.
.
600-1

Electrical
Test
Equipment
.....
.
.
.
....
.
.
.
.
600-2

WIRING
DIAGRAMS
..
.
.
.
.
.
.
.
.
.
........
600-2

Ming
Codes
and
Abbreviations
..
.
...
.
....
600-2

ELECTRICAL
TROUBLESHOOTING
..
.
..
600-3

Voltage
and
Voltage
Drops
..........
.
.
.
.
.
600-4

GENERAL



Electrical
System
Safety
Precautions

A
brief
description
of
the
principal
parts
of
the
electrical
sys-
tem
is
presented
here
.
Also
covered
here
are
basic
electrical
system
troubleshooting
tips
.

Voltage
and
Polarity

The
vehicle
electrical
system
is
a
12-volt
direct
current
(DC)
negative-ground
system
.
A
voltage
regulator
controls
system
voltage
at
approximately
the
12-volt
rating
of
the
battery
.
Al¡
circuits
are
grounded
by
direct
or
indirect
connection
to
the

negative
(-)
terminal
of
the
battery
.
A
number
of
ground
con-

nections
throughout
the
car
connect
the
wiring
harness
to

chassis
ground
.
These
circuits
are
completedby
the
battery

cable
or
ground
strap
between
the
body
and
the
battery
nega-

tive
(-)
terminal
.

Wiring,
Fuses
and
Relays

Nearly
all
parts
of
the
wiring
harnessconnect
to
compo-

nents
of
the
electrical
system
with
keyed,
push-on
connectors

that
lock
into
place
.
Notable
exceptions
arethe
heavy
battery

cables
and
the
starter
wiring
.
The
wiring
is
color-coded
for
cir-

cuitidentification
.

With
theexception
of
the
battery
charging
system,
most

electrical
power
is
routed
from
the
ignition
switch
or
the
bat-
tery
through
the
main
fuse/relay
panel,
located
in
¡he
left
rear

comer
of
the
engine
compartment
.
Fuses
are
color
coded
to

indicate
current
capacities
.

The
relays
and
control
units/modules
are
mounted
in
vari-

ous
places
throughout
the
vehicle
.
See610
Electrical
Com-

ponent
Locations
.

ELECTRICAL
SYSTEM-GENERAL
600-1

Voltage,
measuring
.
.
.
................
.
.
600-4

Voltage
drop,
testing
.
.
.....
.
.....
.
......
600-4

Continuity,
checking
..
.
...
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
600-5
Short
Circuits
.
.
.
.
.
.
.
.
.....
.
...
.
.
.
.
.
.
.
.
.
600-5

Short
circuit,
testing
with
ohmmete'r
.
.
.
.
.
.
.
.
.
600-6

Short
circuit,
testing
with
voitmeter
.
.
.
.
.
.
.
.
.
600-6

TABLES
a
.
Terminal
and
Circuit
Numbers
..............
..
.600-3
Please
read
the
following
warnings
and
cautions
before
do-
ing
any
work
on
your
electrical
system
.

WARNING
-

"
The
cars
covered
by
this
manual
are
equipped
with
aSupplemental
Restraint
System
(SRS)
that
automatically
deploys
one
or
more
airbags
.
Each
airbag
unit
houses
an
explosive
powerful
charge
.
Any
work
involving
the
SRS
system
should
only
be
performed
byan
authorized
BMW
dealer
.
Making
repairs
without
the
proper
knowledge
and
special
test
equipment
may
cause
serious
per-
sonal
injury
.
See
721
Airbag
System
(SRS)
.

"
The
ignition
system
of
the
car
operates
at
lethal
voltages
.
People
with
pacemakers
or
weak
hearts
should
not
expose
themselves
to
the
ignition
sys-
tem
.
Extra
caution
mustbe
taken
when
working
on
the
ignition
system
or
when
servicing
theen-
gine
while
it
is
runningor
the
key
is
on
.
See
120
Ignition
System
for
additional
ignition
system
warnings
and
cautions
.

"
Before
operating
the
starter
without
starting
the
engine
(as
when
making
a
compressfon
test),
dis-
able
the
ignition
system
as
described
in
120
Igni-
tion
System
.

"
Keep
hands,
clothing
and
other
objects
clear
of
the
electric
radiator
coollng
fan
when
working
on
a
warm
engine
.
The
fan
may
start
at
any
tíme,
even
when
the
ignition
is
switched
off
.

GENERAL

600-2



ELECTRICAL
SYSTEM-GENERAL

CAUTION
-

"
Always
turn
off
the
engine
and
disconnect
the

negative
()
cable
from
the
batterybefore
remov-

ing
any
electrical
components
.
Disconnecting
the

battery
may
erase
fault
code(s)
stored
in
control

module
memory
.
Check
for
fault
codes
using
spe-
cial
BMW
diagnostic
equipment
.

"
Prior
to
disconnecting
the
battery,
read
the
bat-

tery
disconnection
cautions
given
at
the
front
of

this
manual
onpage
viii
.

"
Connect
and
disconnect
ignition
system
wires,
multiple
connectors,
and
ignition
test
equipment
leads
only
while
the
ignition
is
off
.

"
Do
not
disconnect
the
battery
with
engine
run-

ning
.

"
Do
not
quick-charge
the
battery
(for
boost
start-
ing)
for
longer
than
one
minute,
and
do
not
ex-
ceed
16
.5
volts
at
the
battery
with
the
boosting
cables
attached
.
Wait
at
feast
one
minute
before
boosting
the
battery
a
second
time
.

"
Do
not
usea
test
famp
that
has
a
normal
incan-

descent
bulb
to
test
circuits
contafning
electronic
components
.
The
high
electrical
consumptionof
these
test
lamps
may
damage
the
components
.

"
Do
not
use
an
analog
meter
.
Use
onfy
a
digital
multimeter
.

"
Many
of
the
solid-state
modules
are
static
sensi-
tive
.
Static
discharge
will
permanently
damage
them
.
Always
handle
the
modules
using
proper
static
prevention
equipment
and
techniques
.

"
To
avoid
damaging
harness
connectors
or
relay
panel
sockets,
use
jumper
wires
with
flat-blade
connectors
that
are
the
same
size
as
the
connec-
tor
or
relay
terminals
.

"
Always
switch
a
digital
multimeter
to
the
appropri-
ate
function
and
range
before
making
test
con-
nections
.

"
Do
not
tryto
start
the
engine
of
a
carwhich
has
been
heated
above176°F
(80°C),
(for
example,
in
a
paint
dryingbooth)
.
Allow
it
to
cool
to
normal
temperature
.

"
Disconnect
the
battery
before
dolng
any
electric
welding
on
the
car
.

"
Do
not
wash
the
engine
while
it
is
runnfng,
or
any-
time
the
ignition
is
switched
on
.

WIRING
DIAGRAMS

Electrical
Test
Equipment

Many
of
the
electrical
tests
described
in
this
manual
call
for

measuring
voltage,
currentorresistanceusing
a
digital
multi-

meter
(DMM)
.
Digital
meters
are
preferred
for
precise
mea-

surements
and
for
electronics
work
because
they
are
generally
more
accuratethan
analog
meters
.
The
numerical

display
is
alsoless
likely
to
be
misread,
since
there
is
no
nee-

dle
position
to
be
misinterpreted
by
reading
at
an
angle
.

An
LED
test
light
is
a
safe,
inexpensive
tool
that
can
be
used

to
perform
many
simple
electrical
tests
that
would
otherwise

require
a
digital
multimeter
.
The
LED
indicates
when
voltage

is
present
between
anytwo
test-points
in
a
circuit
.

CA
UTION-

"
Choose
test
equipment
carefully
.
Use
a
digital

multimeter
with
at
leadt
10
megaohm
input
im-

pedance,or
an
LED
test
light
.
An
analog
meter
(swing-need1e)
ora
test
light
with
a
normal
incan-
descent
bulb
may
draw
enough
current
to
dam-
age
sensitive
electronic
components
.

"
An
ohmmeter
must
not
beused
to
measure
resis-
tance
on
solidstate
components
suchas
controlunits
or
time
delay
relays
.

"
Always
disconnect
the
battery
before
making
re-

sístance
(ohm)
measurements
on
the
circuit
.

WIRING
DIAGRAMS

The
wiring
diagrams
shown
in
Electrical
Wiring
Diagrams

have
been
specially
designed
to
enable
quick
and
efficientdi-

agnosis
and
troubleshooting
of
electrical
malfunctions
.

Wiring
Codes
and
Abbreviations

A
lot
of
information
is
included
in
each
wiring
diagram
if
you
know
how
to
read
them
.
Wire
colors
in
the
diagrams
are
ab-

breviated
.
Combined
color
codes
indicate
a
multi-colored
wire
.
For
example
the
code
BLU/RED
indicates
a
Blue
wire

with
a
Red
stripe
.

Many
electrical
components,
connectors,
fuses,
and

ground
locations
are
identified
using
a
unique
number
.
Each

of
there
numbers
corresponds
to
a
particular
part
in
the
circuit
commonly
found
in
Electrical
Wiring
Diagrams
.

NOTE
-

Sometimes
the
color
of
en
installed
wire
may
be
differ-
ent
than
the
one
on
the
wiring
diagram
.
Don't
be
con-
cerned
.
Just
be
sure
lo
confirm
that
the
wire
connects
lo
the
proper
terminals
.

Wire
color
codes

"
BLU
.........
.
..
..
...
.
.................
Blue

"
BRN
....:....
.
..
..
...
..
...............
Brown

"
YEL
.........
.
..
..
...................
.Yellow

"
GRN
.........
.
..
..
...
.
................
creen

"
G
RY
.......
.
.
.
..
..
.....................
G
ray

"
ORG
.........
.
..
..
...
.
..............
.Orange

"
RED
......
...
.
.
..
.....................
.Red

"
BLK
.........
.
..
..
...
.
................
Black

"
VIO
..........
.
..
...
..
..
.......
.
.......
Violet

"
WHT
.........
.
.
....
.
...
:..............
White

Table
a
.
Terminal
and
Circuit
Numbers

Number



1
Circuít
description

1



j
Low
voltage
switched
terminal
of
coi¡

4



1
High
voltage
center
termina¡
of
coi¡

+x



Originates
atignition
switch
.
Supplies
powerwhen
the
ignition
switch
is
in
the
PARK,
RUN,
or
START
position

15



Originates
atignition
switch
.
Supplies
powerwhen
ignition
switch
is
in
RUN
or
START
position

30



Battery
positive
(+)
voltage
.
Supplies
power
whenever
battery
is
connected
.
(Not
dependent
on
ignition
switch
position,
unfused)

31



1
Ground,
battery
negative
(-)
terminal

50



Supplies
power
from
battery
to
starter
solenoid
when
ignition
switch
isin
START
position
only

+54



Originates
atignition
switch
.
Supplies
power
when
ignition
switch
isin
the
RUN
position
only

85



1
Ground
side
(-)
ofrelay
coil

86



1
Power-in
side
(+)
ofrelay
coil

87



1
Relay
actuatedcontact

D



Alternator
warning
light
and
field
energizing
circuit

ELECTRICAL
SYSTEM-GENERAL
600-
3

Additional
abbreviations
shown
in
the
wiring
diagrams
are

given
below
.

Abbreviations

"
ABS
........
.
...
.
...
.
..........
antilock
brakes

"
A/C
........
.
...
..
..
.
.........
.airconditioning

"
AST/ASC+T
.......
...
.
.
.......
al¡
season
traction

"
CONV
.......
.
.
...
.................
convertible

"
DME
........
.
.
...
.......
digital
motor
electronics

"
ECM



.......
.
...
..
..
.
..
electronic
control
module

"
EWS/EWS
II
......
...
.
.
coded
driveaway
protection

"
SRS
........
.
supplemental
restraint
system-airbag

"
TCM
........
.
..
....
.
transmission
control
module

"
ZKE
(94-98
models)
..
..
.
...
central
body
electronics

"
ZVM
(92-93
models)
...
.
.
..
.
.......
central
locking

ELECTRICAL
TROUBLESHOOTING

Most
terminals
are
identified
by
numbers
on
the
compo-

nents
and
harness
connectors
.
The
terminal
numbers
for
ma-



Four
things
are
required
for
current
toflow
in
any
electrical

jor
electrical
connections
are
shown
in
the
diagrams
.
Though



circuit
:
a
voltagesource,
wires
or
connections
to
transport
the

many
terminal
numbers
appear
only
once,
severa¡other
num-



voltage,
a
load
or
device
that
uses
the
electricity,
and
a
con-
bers
appear
in
numerous
places
throughout
the
electrical
sys-



nection
to
ground
.
Most
problemscanbefound
using
a
digital

tem
and
identify
certain
types
ofcircuits
.
Some
of
the
most



multimeter
(volt/ohm/amp
meter)to
check
for
voltage
supply,

common
circuit
numbers
are
listed
below
in
Table
a
.



for
breaks
in
the
wiring
(infinite
resistance/no
continuity),
orfor

a
path
to
ground
that
completesthe
circuit
.

Electric
current
is
logical
in
its
flow,
always
moving
from
the

voltage
sourcetoward
ground
.
Electricalfaults
can
usually
be

located
through
a
process
of
elimination
.
When
troubleshoot-

ing
a
complex
circuit,
separate
the
circuit
into
smaller
parts
.

The
general
testsoutlined
below
may
be
helpful
in
finding

electrical
problems
.
The
information
is
most
helpful
when

used
with
the
wiring
diagrams
.

Be
sure
to
analyze
the
problem
.
Use
the
wiring
diagrams
to

determine
the
most
likely
cause
.
Getan
understanding
of
how

the
circuit
works
by
following
the
circuit
from
groundback
to

the
power
source
.

When
making
test
connections
at
connectors
andcompo-

nents,
use
care
to
avoidspreading
or
damaging
the
connec-

tors
or
terminals
.
Some
tests
may
require
jumper
wires
to

bypass
components
or
connections
in
the
wiring
harness
.

When
connecting
jumper
wires,
use
bladeconnectors
at
the

wire
ends
that
match
the
size
of
the
terminal
being
tested
.
The

small
interna¡
contacts
are
easily
spread
apart,
and
this
can

cause
intermittent
or
faultyconnections
that
can
leadto
more

problems
.

ELECTRICAL
TROUBLESHOOTING

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
.

Continuity,
checking
Short
Circuits

from
Battery

CAUTION-

Use
only
a
high
quality
digital
ohmmeter
having
high
input
impedance
when
checking
electronic
componente
.
The
internal
power
source
used
in
most
analog
(swing-need1e)
meterscan
damage
solidstate
components
.

0013239

Fig
.
2
.



Digital
multimeter
being
used
to
check
for
voltage
drop
across
a
switch
.

The
continuity
test
can
beused
to
check
a
circuit
or
switch
.
Because
most
automotive
circuits
are
designed
to
have
little

or
no
resistance,
a
circuit
or
part
of
a
circuit
canbe
easily

checked
for
faults
using
an
ohmmeter
.
An
open
circuit
or
a
cir-

cuit
withhigh
resistance
will
not
allow
current
to
flow
.
A
círcuit
with
little
or
no
resistanceallows
current
to
flow
easily
.

When
checking
continuity,
the
ignition
should
be
off
.
On
cir-
cuits
that
are
powered
at
all
times,
the
battery
should
be
dis-
connected
.
Using
the
appropriate
wiring
diagram,
a
circuit
can
be
easily
tested
for
faulty
connections,
wires,
switches,
relays,
and
engine
sensorsby
checking
forcontinuity
.
For
a
continu-
ity
check
on
a
brake
light
switch,
see
Fig
.
3
..

A
short
circuit
is
exactly
what
the
narre
implies
.
The
circuit
takes
a
shorter
paththan
it
was
designed
to
take
.
The
most

common
short
that
causes
problems
is
a
short
to
ground

where
the
insulation
on
a
positive
(+)
wire
wears
away
and
the

metal
wire
is
exposed
.
When
the
wire
rubs
against
a
metal

partof
thecar
or
other
ground
source,
the
circuit
is
shorted
to
ground
.
If
the
exposed
wire
is
live
(positive
battery
voltage),
a

Puse
will
blow
and
the
circuit
may
possibly
be
damaged
.

ELECTRICAL
SYSTEM
-
GENERAL
600-
5

Brake
light
switch

Brake
pedal
in
rest
position

Q

Brake
pedal
depressed
Brake
light
switch

Fig
.
3
.



Brake
light
switchbeing
tested
for
continuity
.
With
brake
ped-
alin
rest
position
(switch
open)
there
is
no
continuity
(infinite
ohms)
.
With
pedal
depressed
(switch
closed)
there
is
continu-
ity
(zero
ohms)
.

Shorts
to
groundcanbe
located
with
a
digital
multimeter
.
Short
circuits
are
often
difficult
to
locate
and
may
vary
in
na-
ture
.
Short
circuits
can
befound
using
a
logical
approach
based
onthe
current
path
.

CAUTION
-

"
On
circuits
protected
with
high
rating
fuses
(25
amp
and
greater),
the
wires
or
circuit
compo-
nents
may
be
damaged
before
the
fuse
blows
.
Always
check
for
damage
before
replacing
fuses
of
this
rating
.

"
When
replacing
blown
fuses,
use
only
fuses
hav-
ingthe
correct
rating
.
Always
confirm
the
correct
fuse
rating
printed
on
the
fuselrelay
panelcover

DC

ELECTRICAL
TROUBLESHOOTING