Relay test

Relays are built into many electrical circuits. The switching relay works like a switch. When a consumer of electricity is turned on manually via a switch, the relay receives a command to supply current to the consumer. Of course, it would be possible to supply current to the consumer directly through the switch from the battery. However, for all consumers requiring high current, an intermediate relay is included so as not to overload the switch and guarantee the circuit from a short circuit.

Checking the switching relay

The supply of current to the relay occurs when the corresponding consumer is turned on. Due to the switching current, the electromagnet coil inside the relay attracts the contact and thus closes the electrical circuit of the operating current. The operating current flows further through the relay to the consumer.

The easiest way to check the performance of the relay is to replace it with a good one. This is how they do it at the station. Since the motorist only in very rare cases has a new relay at his disposal, the following sequence of operations is recommended:

• Pull the relay out of the board.
• Turn on the ignition and the appropriate switch.
• First, use a voltage tester to determine if voltage is applied to the positive terminal (+) relay boards. To do this, connect one electrode of the tester to ground (-), and carefully insert the other electrode with a sharp end into the terminal. If the light diode of the device lights up, then the voltage is applied. If the device shows no voltage, guided by the electrical circuit, find an open circuit in the area from the positive pole (+) battery to the terminal.
• Make a jumper from a piece of insulated wire, cleaning the ends of the jumper to a shine.
• Connect the positive terminal with this jumper (+) relay boards (This terminal is always supplied with voltage from the positive pole of the battery) with relay output terminal.

This operation practically does the same thing that a good relay does. Where the relay board terminals are located can be determined by the color of the wires or by using the electrical diagram.


If, for example, the main beam lights up when the jumper is installed, it can be concluded that the relay is faulty.

If the high beam does not light up, it is necessary to find out if the headlight ground connection is correct (-). Then, guided by the electrical circuit, find and repair an open in the wiring from the relay terminal to the main headlights.

If required, install a new relay.

Attention: If a malfunction in the electrical circuit with a relay occurs only from time to time, then the cause is usually due to a defect in this relay. In this case, the relay contact remains closed or open, while the rest of the time the relay functions flawlessly. If this kind of malfunction occurs, it is easy to knock on the relay housing. If the relay trips as a result, it should be replaced.