Please refer to Sect. D 5, DDS diagnosis instrument, as far as “DDS” tester is concerned.

This instrument can take resistance, voltage and current values. Multimeters are usually gathered into two big families: analogue and digital display multimeter. An analogue multimeter has a pointer display. Display dial shows different measurement scales. Digital ones have a dial on which digits for taken value are indicated. A selector or a set of outlets for both terminals allow you to set unit of measurement, i.e. volt, ampere or ohm. Sometimes the full scale value should also be set. If a voltage value of 12V needs to be taken, select a full scale which is as close as possible to this value: for example 15V or 20V. A 10V full scale is not correct. The same applies if amperes or ohm values should be taken. Sometimes the instrument automatically sets the full scale value. Never exceed the max. value allowed by the instrument when measuring volts or ampere.

The “DDS” (Sect. D 5, DDS diagnosis instrument) can work as a digital multimeter.

Always connect multimeter terminals in parallel with the power supplied part, for example with two wires to a lamp, to a relay, to a control unit or with both battery poles. Voltage values are constant over time for direct voltage or variable for alternate voltage. Direct voltage include a negative and a positive pole. For this reason, also the type of voltage should be selected on the multimeter. (= is the symbol for direct voltage; ~ is the symbol for alternate voltage).

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.

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 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). 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.

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 injury. 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.