When using an LED in a circuit, the exact working voltage is not extremely important. The most important thing is the current flow through the LED. The current through the diode must be limited by a series resistor. An LED has a specified maximum continuous current rating. Most LEDs can pass 20 milliamps continuously without damage but it is not necessary to use the maximum rated current. An LED will light with much less current. The difference between high current and low current will be the brightness of the LED. To decide what resistor value is needed, you subtract the working (forward) voltage from the power supply voltage and divide that number by the desired current flow.
Working voltage (Vf)=1.8 volts
A 680 ohm resistor will limit the current to a safe level although I would probably use a 1000 ohm in a vehicle because the charging system voltage would be higher than 12 volts. Any resistor between 680 and 4700 ohms would probably work fine. Choose a resistor with a power rating greater than or equal to the power dissipation given by the calculator above.
The diagram below shows the parts of an LED.
You must also know that an led has polarity. This means that the positive and negative terminals must be connected correctly for it to operate properly. As you see in the diagram below, if the polarity is reversed, the LED will NOT light. If the reverse voltage is beyond what the LED was designed to handle, it may be damaged. Click on the 2 buttons in the demo below to see the LED operation with either polarity.
The picture below shows a few different styles.
