bulb NISSAN ALMERA N15 1995 Owner's Manual

HOWTOPERFORM EFFICIENT DIAGNOSIS FORANELECTRICAL INCIDENT
Circuit Inspection (Cont'd)
VOLTAGE DROPTESTS

Voltage droptests areoften usedtofind components orcircuits whichhaveexcessive resistance. A
voltage dropinacircuit iscaused byaresistance
whenthecircuit isin operation.

Check thewire inthe illustration. Whenmeasuring resistancewithohmmeter, contactbyasingle strand
of wire willgive reading of0ohms. Thiswould indicate agood circuit. Whenthecircuit operates, this
single strand ofwire isnot able tocarry thecurrent. Thesingle strand willhave ahigh resistance tothe
current. Thiswillbepicked upasaslight voltage drop.
Unwanted resistance canbecaused bymany situations asfollows:
Undersized wiring(single strandexample)
Corrosion onswitch contacts
Loose wireconnections orsplices.

If
repairs areneeded alwaysusewire thatisof the same orlarger gauge.

Measuring voltagedrop-Accumulated method

1. Connect thevoltmeter acrosstheconnector orpart ofthe circuit youwant tocheck. Thepositive lead
of the voltmeter shouldbecloser topower andthenegative leadcloser toground.
2. Operate thecircuit.
3. The voltmeter willindicate howmany voltsarebeing usedto"push" current through thatpart ofthe
circuit.

Note inthe illustration thatthere isan excessive 4.1volt drop between thebattery andthebulb.
Symptom: Dimbulb orno operation
Switch Connectionwith
high resistance

l ;

--

------------------~

--
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~~~~ I

-, OVI

11.9V:
'I

I
Load)

--

12V
DMM
Battery
Ground

o

(zero) ohm
resistance
between switch
and bulb

t
•
__
Ground
SGI848
Measuring voltagedrop-Step bystep

The step bystep method ismost useful forisolating excessive dropsinlow voltage systems (suchas
those in"Computer ControlledSystems").
Circuits inthe "Computer ControlledSystem"operateonvery lowamperage.
The (Computer Controlled) systemoperations canbeadversely affectedbyany variation inresistance
in the system. Suchresistance variationmaybecaused bypoor connection, improperinstallation,
improper wiregauge orcorrosion.
The step bystep voltage droptestcan identify acomponent orwire withtoomuch resistance.

GI-26