for faults using an ohmmeter. An open
circuit or a circuit with high resistance
will not allow current to flow. A circuit
with little or no resistance allows
current to flow easily.
When checking continuity, the ignition
should be off. On circuits that are
powered at all times, the battery should
be disconnected. Using the appropriate
wiring diagram, a circuit can be easily
tested for faulty connections, wires,
switches, relays and engine sensors by
checking for continuity.
For example, to test brake light switch
for continuity:
With brake pedal in rest position
(switch open) there is no
continuity (infinite
).
With pedal depressed (switch
closed) there is continuity (0
).
Short circuits
Short circuits are exactly what the
name implies. The circuit takes a
shorter path than 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 part of the car or other ground
source, the circuit is shorted to ground.
If the exposed wire is live (positive
Electrical System - General
http://ebahn.bentleypublishers.com/BMW/3/E46/Repair%20Manuals/6...
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