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12V Car flasher to trun on led, at the same time Flashing is on, Led is on.

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New Member
What I would like to know, can I hook up electronics to my car's right turn light. Hook into the trailer wiring plug. So when the flasher is on, A led is on. So (on and off and on and off with the can's flasher), at the same time A led is on. When flasher is off led is off.

Would A resistor, capacitor, pot, hooked to the (G) on A MOSFET transistor and the other end's hook to ground of the resistor,capacitor,and pot. The (S) to ground and the (D) would have A relay to trun on and off the led or 3.3v to A Microcontroller.

Would some thing like that work, someone might know?

What I am trying to do is when the right or left turn is flashing, it would switch A microcontroller on with 3.3V.

(on)010101010101010101010(off)0000000000000000000 Right turn light
(on)111111111111111111111(off)0000000000000000000 Led or Microcontroller
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New Member
What's the difference between the "I" LED and the "A" LED? Which LED is the "A" relay attached to? Usually a MOSFET has one each "S", "G" and "D" terminals. I think you have written two "S" terminals by mistake.

Your first description appears to ask for the LED to be on exactly the same time as the right turn light. Your second description looks like it is always on?

This could be simple depending on which car you have. Do you have the service manual with a wiring diagram?


Well-Known Member
Most Helpful Member
As mneary states, it could be very simple depending upon the vehicle.

Think what happens when a turn signal stalk is operated.......the stalk operates a switch which stays closed until the cancelling mechanism (or the driver) returns the stalk to the neutral position. The on/off cycle is not handled by the switch, it is handled by a flasher unit, or more recently, a BCM - Body Control Module, or something similar.

Depending upon the complexity of the system installed in the vehicle, it just may be a simple task of tapping into the left & right switch signal wires and hooking up the LED's via a suitable resistor.....

What is the purpose for adding an additional LED?
Does the vehicle instrument cluster not already have a 'telltale' fitted as standard?

Your post is a little confusing...if you would like the LED to flash, you would tap into the wires going to the lamps. If you would like the LED to remain constantly lit whilst the turn signals flash, you would tap into the switch signal wires.



Well-Known Member
Usually it goes like this;
+12v -> flasher device (SPST) -> turn signal switch (SPDT centre off) -> 12v 20w light bulbs.

So the whole power to the system is "flashing". You could use a MOSFET etc and a cap on it's gate that will keep it turned on for the low period of the flash cycle. That would work ok, but it would stay on for a few seconds after the turn signal was turned off.
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