ELECTRICAL SYSTEM
10
Measurement of resistance values and electrical continuity
Resistance measurements must be taken only when the electrical device or section of the circuit is not
powered and isolated from the main electrical system (i.e. not connected to the main electrical system).
These measurements can be utilised to check the resistance value across several sensors. For example,
after disconnecting the electrical wiring to the rpm/ignition - injection system timing sensor (on the camshaft
drive gear) the relative internal resistance can be checked by connecting a multimeter to its terminals. This
makes it possible to check the electrical continuity of the winding inside the sensor (a reading of infinite
resistance indicates that the winding is interrupted). Resistance measurement can also be used to check the
continuity of sections of the electrical circuit or relay type switches. For example, to check the condition of a
section of the electrical circuit between two connections, disconnect the connections and connect the
terminals of the multimeter to the ends of the electrical cable in question to check that the specified
resistance value is present. If this value is close to zero (i.e. lower than approximately 0.3 ohm) this means
that the cable is not interrupted. Some instruments feature an audible signal that is emitted when the
resistance approaches a value of zero. The same procedure must be adopted to check whether, for
example, two contacts of a switch (relay or manual type) are making the contact correctly when closed. In
this case the terminals of the multimeter must be connected to the switch terminals, checking that the
resistance value is close to zero (or listening for the audible signal) when the switch is closed. To check that
the multimeter is functioning correctly in “electrical continuity test” mode, short out the two test probes. The
resistance value indicated must be almost nil and the audible signal must be activated.
Protections and precautions
The multimeter is equipped with protective fuses and batteries. These components must always be in perfect
condition to ensure that the instrument is functioning correctly. When making electrical measurements
always use the maximum caution to avoid short circuits, which can otherwise cause irreparable damage to
the electrical system and constitute a personal injury hazard. All maintenance work must be performed
exclusively when the system is not live (disconnect the battery in advance). NEVER connect the multimeter
in parallel to make current measurements, and NEVER connect it in series to carry out
voltage measurements.
Sub 10-41
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