Newbie wiring an LED with 6v and 12v question

[Phil.g.]

Hi all,
I'm very new to this seen, but Im eager to learn,
I am trying to wire an led on my cars dashboard for main beam, the only thing is, there are 2 different volts on the power wire.
When i put the lights on it has 6.4v and when I put the main beam on its has 12.4
Is there anything I can do to make the led only light up when there is 12.4v only?
Any help would be great,
Thanks,
Phil.

[David]

Where are you measuring these voltages? If your car has the common headlamp bulbs with two filaments, you should measure 12v between the main beam filament connector and chassis when it is on, and 0v when it is off.

[Phil.g.]

I took it from the main beam LED in the dash, I was going to take a wire from further down the loom to the relay for the main beam bulb, but wondered if there was another way first.

[David]

It sounds as if there is a complication with the way in which the existing LED is wired. Possibly the simplest solution is to take a separate feed from the main beam relay (i.e. the feed to the bulb itself) to the new LED with its own series resistor. There is a useful LED resistor calculator on this website.

[Phil.g.]

Yeah I was thinking that, I have a few different resistors so I'll sort it, I was just trying an option that could be soldered on the led inline maybe, I Didn't know if there was anything or not, I'll stick with the original plan like you said, with a wire from the main beam bulb to the led,
thanks anyway for the reply
I'll be quizzing you soon again,
All the best,
Phil.

[Pauldf]

You could stick a 6.8v zener diode in series with an LED and resistor. For a 30mA LED 150ohms resistor will be about right.

[Phil.g.]

Ahaa thats what I was hoping for, something like that, So does it go on the + or - side of the led and the same side as the resistor, I'll look now online for them, thanks very much PAULDF

[Phil.g.]

I've just looked on YouTube and I see how they work now, I'll get some bought and do some testing as to what resistor I need.
Many many thanks again PAULDF.

[Pauldf]

It doesn't really matter which side of the LED you put them on, personally i'd do from +ve, zener, resistor, LED, -ve.
Just remember the zener goes the opposite way around to a conventional diode, the band on it faces the +ve.

[Phil.g.]

Right, I'll do that when they arrive and I'll update here when I have it working, I can't thank you enough for your knowledge PAULDF
thanks again,
Phil.