Voltage drop, testing
Voltage drop can only be checked
when there is a load on the circuit,
such as when operating the starter
motor or turning on the headlights. A
digital multimeter should be used to
ensure accurate readings.
Connect digital multimeter positive lead
to positive (+) battery terminal or a
positive power supply close to battery
source.
-
Connect digital multimeter
negative lead to other end of cable
or switch being tested.
-
With power on and circuit working,
meter shows voltage drop
(difference between two points).
This value should not exceed 1
volt.
Note:
The maximum voltage drop in an
automotive circuit, as recommended by
the Society of Automotive Engineers
(SAE), is as follows: 0 volts for small
wire connections; 0.1 Volts for high
current connections; 0.2 volts for high
current cables; and 0.3 volts for switch
or solenoid contacts. On longer wires or
cables, the drop may be slightly higher.
In any case, a voltage drop of more
than 1.0 volt usually indicates a
problem.
Continuity, checking
Continuity tests can be used 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 can be easily checked
Electrical System - General
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