A thought, all I know about newer (computerized) automobiles would fit on one fingernail. Practical measurement is the bottom line for a computer input. Take the lamp designated, hook it across the battery with the engine running and measure the current. When we speak of a 12 volt system, or a 12 volt battery, we are actually speaking of a voltage of 12.5-13.2. The charging system is a little higher still, often as much as 15 volts. Automotive batteries have six "cells" of 2.2 volts, making a nominal fully charged battery 13.2 volts. And lamps have an inverse resistance curve. They will measure low resistance, almost a short, when cold. They must be tested/measured hot.
Try a nominal resistance, whatever seems to fit right. E=IxR and P=ExI. . . Connect two diodes in series with the resistor. 1N4001, any 1N400x will work. There will be a constant drop of 0.7 volts across one diode. That 0.7 volt drop is called the "Fermi" drop and is constant regardless of current or voltage in the circuit. Two in series will drop 1.4 volts. Most LEDs will light on this 1.4 volts without a resistor. If you're nervous, use a 100 ohm ballast with the LED. It is not really necessary but for a novice will quiet fears. It may require a third diode, 2.1 volts, making the LED ballast mandatory. That will be a function of the particular LED, primarily the color, which will vary it somewhat.
Tune the main resistor to get the same current that is on the lamp. Give or take a few ohms to the nearest standard size. Connect the LED across the 1N400x diodes, essentially in series with the resistor. That should light the LED with the proper current for the lamp. Lamp current is a common control mechanism in automotive systems, particularly with a two prong flasher in the turn signals. The above circuit will duplicate the current drawn by the lamp yet use an LED as visual indication.
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