The DRL (Daytime Running Light) system turns the headlights on while the engine is running in the daytime. This means that the headlight bulbs are turned on at all times, which shortens bulb life. To prevent this, the system’s circuitry reduces the light intensity of the headlights while DRL is on. This is accomplished mainly by one of the following main three types of circuitry.
(1)Type in which light intensity is reduced by DRL resistor
Light intensity is reduced via the DRL resistor while the DRL system is operating.
(2)Type in which light intensity is reduced through series connection of headlights
Light intensity is reduced by having current flow in series of the left-hand and right-hand headlights while the DRL system is operating.
(3)Type in which light intensity is reduced by duty control in DRL main relay
Light intensity is reduced by a duty control circuit in the DRL main relay while the DRL system is operating.
DRL operates when the engine is running and while the parking brake is released.
In order to set these conditions, input signals from the alternator or the parking brake switch are usually used. However, some models have no parking brake signal. In some models, the taillights come on at the same time.
This explanation is based on the type with a DRL resistor.
(1)When the engine is started and while the parking brake lever is released, the DRL main relay turns on the headlights. If the light control switch is in the OFF or TAIL position and the dimmer switch is in the LOW position, the DRL relay turns off and current moves through the DRL resistor. As a result, the headlights come on with light intensity reduced to 80-85%.
(2)If the light control switch is moved to the HEAD position, the DRL No. 2 relay turns on and current flows to the headlights without passing through the DRL resistor. The headlights come on at normal intensity.
The DRL No. 2 relay turns on even while the dimmer switch is in the HIGH or FLASH position, so the headlights will also come on at normal intensity.