Example: When the manual switch is turned on, the relay receives the command to connect the voltage to the high beam headlights. Of course, it would be possible to supply the voltage from the battery to the high beam headlights directly via the switch. However, for all powerful consumers, an intermediate relay is switched on in order not to overload the switch or to ensure a shorter voltage transmission path. In addition to the switching relay, there are also function relays, for example for the windscreen wiper system or a relay for the warning sound signal for the external lighting.
Checking the on-relay
When the corresponding consumer is switched on, the relay is activated, i.e. under the influence of the switching current, the electromagnetic coil inside the relay attracts the contact and thus supplies the "working current" to the current circuit. The working current flows through the relay to the consumer.
The easiest way to check the relay operation is to replace it with a known good one. This is done at a service station, but at home you don't always have an extra relay, so the following method is recommended for the so-called turn-on relays, as they are often called when applied to turning on the main and fog lights.
Remove the relay from the socket.
Turn on the ignition and the corresponding switch.
First, check for voltage on the corresponding terminal (+) with a tester. To do this, connect one wire of the tester to ground and carefully insert the other into the terminal. If the tester lamp lights up, there is voltage. If there is no voltage, find a break in the electrical circuit between the battery and the terminal.
Make a jumper from insulated wire, strip the ends.
Connect the jumper on the relay block from the (+) terminal of the battery, which is always under voltage, to the output contact of the relay. This achieves the effect as if a replacement was made with a known good relay. The location of the terminals on the relay block is determined by the color of the wires or by the electrical diagram.
If, with a jumper, the high beam headlights light up, for example, the relay is faulty.
If the high beam does not work, find out if the headlights are connected to the ground. Then, using the electrical diagram, find and fix the wire break.
Original source of information: MITSUBISHIMAN
If necessary, install a new relay.