Newbie Help with LED's

Thread Starter


Joined Mar 26, 2018
Hello Folk's

I am looking to find some information about running 1 LED from 6v Pos Gnd.

The application is on a 1931 Ford Model A Tudor that I added turn signals to. The car is 6v Pos. Ground. Wiring is complete and functional and work off of a momentary toggle switch. The system can be seen here, ...

My Goal is to have turn indicators INSIDE the car pointing down onto the floorboard, Red for left turn and Green for a right turn. I also would like them to not use their full potential, more or less muting the lights output electronically. The switch is mounted under the dash and is not visible from inside the car and have to flick it with my finger under the dash, so I really don't want flashing lights to be to noticeable and really only for my viewing as a reminder they are on.

Thank You


Joined Dec 2, 2017
You could grab some pre wired 12 volt LEDs and place them in parallel with the bulbs you installed, they would flash along with the other bulbs, and only be using half power.

Oh said only one LED...well you could get a bi-color LED and wire the resistors manually, just be sure to get a common anode.


Joined Aug 1, 2013
For garden variety low cost LEDs, either separate red and green or a bi-color red-green in a three-lead package, assume the forward voltage drop (Vf) across an LED is 2.0 V. It is slightly less for red and slightly more for green, but that is a safe value. There will be some additional voltage drop across the turn signal switch and/or flasher system, especially if these are solid state circuits, but those will be low values and can be assumed to be 0 V as a starting point. So, 6 V system - 2 V Vf = 4 volts across the current limiting resistor. For a typical operating current of 20 mA, that calculates out to 200 ohms. 220 ohms is a bit more common value. Power in the resistor will be Watt's Law, E^2 / R, or 16/220 = 73 mW, so a standard 1/4 W part will work well in this application. For less brightness, increase the resistor value.

If you are using a single, bi-color LED, then you need to pay attention to the internal connection. Are you switching one end of the LED to 6 V, with the other end connected to GND? If so, use a common cathode LED. The resistor goes between the cathode connection and GND, and you switch either anode to Vbat. If you are switching the ground, use a common anode LED with the resistor between the anode and Vbat.