Testers
How to measure current
Always connect multimeter terminals in series with the power supplied part. For example: disconnect a
wire powering a lamp and connect a terminal with the end of the disconnected wire and the other
terminal with the lamp. Position the light switch to on, the lamp will turn on and the instrument will
show the value for absorbed current, that is the value for the current flowing into the wire. Important:
when connecting in series, connect and disconnect when parts are not live. Never connect or
disconnect if the part is powered. Always ensure that tester terminals are safely connected in series
with the electric device and that cannot disconnect by accident.
How to measure resistance and electric continuity
Measure resistance value only when the electric part or system section is not live and is insulated from
the main electric system, i.e. disconnected from the main electric system. Taken values may be useful
to check resistance value of some sensors. For example, disconnect engine rpm and timing sensor -
facing the timing control gear- from the ignition-injection system and check its inner resistance value
by connecting the multimeter to its terminals. In this way, sensor inner coil is checked for continuity (if
coil is broken, resistance is infinite). Resistance value can also help when checking the continuity along
electric system sections or in switches or relays. To check a section of the electric system included
between two connections, disconnect those connections, connect multimeter terminals to both ends of
the power cable and read displayed resistance value. If close to zero (under approx. 0.3 Ohm) the
cable is not broken. Some instruments emit a beep when the value is close to zero.
Follow the same procedure to check whether two contacts of a switch, be it a relay or a manual switch,
close properly. Connect the multimeter terminals to the switch terminals and ensure that resistance
value is close to zero once the switch is closed (also hear the beep).
The resistance value should be infinite once the switch is open.
Short-circuit multimeter terminals to ensure that it is in "electric continuity check" mode. The
resistance value should be close to zero and relevant beep should be emitted.
Protections and precautions for a proper use of the multimeter
The multimeter is fitted with fuses and batteries. They should always be in perfect operating conditions
to ensure proper operation of the instrument. When using the multimeter, pay utmost care not to
cause short circuits as they may irreparably damage the electric system or cause injuries. Service
parts only when voltage is off: disconnect the battery first. NEVER connect the multimeter in parallel to
take current values. NEVER connect the multimeter in series to take voltage values.
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