Voltage, current and resistance measurement

If you want to know if the various electrical consumers in your Focus are in order, then more than just an auto electrician can help you: there are a number of test devices in specialized stores with which you can check the electrical equipment yourself.

Pilot lamp (with needle contact). With its help, you check if there is voltage in the electrical circuit: the brighter the lamp burns, the higher the voltage. Simply pierce the insulation of the wire to be tested with the needle of the lamp. Attach the clamp on the lamp wire to the mass (e.g. to terminal 31 (negative pole) battery, motor housing, bare metal of the body, etc). Be careful: the test lamp consumes a lot of power and is therefore not suitable for measurements in electronic assemblies (e.g. in the engine control unit). In this case, you should use a voltage indicator with LEDs. Voltage indicator with LEDs. Depending on the model, the device induces a constant or alternating voltage from 6 to 700 V approx. Voltage indication is carried out optically via LEDs.

multimeter (universal device). They measure voltage, current (constant and variable) and resistance. Better devices with digital indication. The multimeter is usually powered by an internal battery.

Voltage measurement. In order, for example, to measure the quiescent voltage of a battery with a multimeter, you must use the black wire marked with «-», connect to battery terminal 31 (negative pole) or to the mass. red wire «+» measuring device is connected to terminal 30 of the battery (positive pole) or to the wire being measured. If the meter shows only about 10.4 V, then this indicates a defective battery cell. Check battery performance when starter is actuated - measured at 5V (±0.5 V) means the battery is bad.


Current measurement: to do this, open the electrical circuit and connect a measuring device to it. As a rule, it is sufficient if you disconnect the corresponding plug contact in your Focus and then simply connect the measuring device between the connector and the contact tab. Be careful: always remember the measuring range of your multimeter. In consumers such as a starter, very high currents flow - your device may suffer from them.

Resistance measurement: With a multimeter, you can check if there is conductivity in the wire or switch. If the current flows unhindered, then the device will show a resistance value of 0. If there is a defect in the wire or switch, the measured resistance value will be equal to infinity (∞). In addition, you can measure the internal resistance of electrical components with a multimeter.