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See the wires running up to the top corners? The wires run from circuit board to the upper corners

You are likely best to take out that circuit board and actually identify the components- specifically the regulator.

Typical circuit for 78XX voltage regulator from AC incoming power on the left. RL is the load. This circuit in the car appears to not have any capacitors for DC smoothing.

That voltage determines the resistor value when using LEDs

Also, we need an understanding of if that board has resistors or other current limiting in series with the LEDS- otherwise, you need to put them in series with the the LEDs

LEDs have a forward voltage before they conduct- that is NOT the same thing you are asking, AND, they need EXTERNAL current limiting (AKA a resistor in series or some other control for current).

LED- acronym- Light Emitting Diode- so it's a diode. Once it begins conducting- that basically is full tilt what the power source can provide.

https://www.digikey.com/en/res...-led-series-resistor

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Those look like GOW bulbs to me if we're talking about these.

Which given what appears to be maybe a CV (constant voltage) but no indication or resistors needed for constant current or current limiting - why I went into the explanation about LEDs and resistors.

I''m obviously making assumptions and guessing- just like others given I do not have the car in front of me and going off a picture.

But again, a first glasce, we need LEDs with resistors, and in order to figure out that resistor value- ideally knowing the circuit board would help.

That is clearly an incandescent grain of wheat bulb. I can see the filament.

KA317 is the LM317 equivalent. That device can either be used in constant voltage or constant current mode but given incandescent bulbs, and not maxing the voltage out- indicates likely CV mode.



Given the low measured regulated voltage of 6.7V and being white LEDS typically are above 3V, putting them in series output is right on that limit of possibly not working. So for 20mA I get a 165 Ohm resistor. Or if running the 2 LEDS in parallel and single resistor, then roughly 100-82 Ohms.

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Last edited by Vernon Barry

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