Trying to get a small LED light to blink on & off so it looks like there is an alarm system in the car. I've tried to use a regular flasher out of a car. The LED has a power lead and ground lead. Ran power to one flasher terminal, connected the LED to the other flasher terminal and the LED ground to ground. It lights the LED but no flashing. Switched the wires around on the flasher. Same results. Any ideas?

Thanks for the help!

Mark 66SS

I think you can buy "fake" alarm LED's, probably ebay, or a real alarm store.

I don't think they pull enough current to make an ordinary Flasher work.
http://www.spaghettiengineering.com/comersus/store/comersus_viewItem.asp?idProduct=34

Radio Shack sells blinking LED's for less than $2.
http://www.radioshack.com/product/index.jsp?productId=2117837&tab=summary (http://www.radioshack.com/product/index.jsp?productId=2062553)
It's a 3 volt LED, so you need to wire it in series with a resistor.

Bought the LED I have from Radio Shack. Saw the blinking ones but they were no help on how to make them work on a 12V system. Can you give me more details on what size resistor and how to wire it in series?

Thanks!

Bought the LED I have from Radio Shack. Saw the blinking ones but they were no help on how to make them work on a 12V system. Can you give me more details on what size resistor and how to wire it in series?

Thanks!

Are you going to allow it to be on all the time, even when driving? If not, you need to devise a circuit to turn it off (unless you're just going to install a hidden toggle switch).

If it's just going to be on when the car sits (not running). Figure 12.65 volts (a well charged battery sitting idle).

12.65v-2.25v (the 2.25 is the typical application voltage of the LED) = 10.4 volts that needs to be dropped.

The specs say the maximum current is 90mA (way to high IMHO). So figure on an industry standard of 20mA (20 milliamps aka 20/1000th of an amp).

10.4/.020=520 ohms. 560 ohms is a close radioshack resistor. Part Number: 271-1116

Wire the resistor in series with one leg of the blinking LED. Voila.

I guess you asked about series wiring too. :confused:

The longer lead on the LED should be positive. Connect that "leg" to one end of the resistor. Connect the other end of the resistor to a +12 volt source. Connect the shorter "leg" of the LED directly to a good clean ground. If both legs of the LED look the same, carefully look at the "skirt" of the LED where the legs come out. One side should have a squared off notch or flat side. This flat side corresponds with the (-) Leg that needs to go to ground.
Do not run an LED without a resistor or you'll blow it up.

I set up a flashing LED to simulate an alarm in my 70 last summer. I tried to find what I needed at Radio Shack but all of the LEDs they had would not handle 12v. I went to a local electronics store called Fulton Electric that specializes in anything elctrical... switches of all sorts, LEDs, cable, wires, etc. and bought a 12v LED that is already set up to flash. It cost less than $5.

I set it up so that when the key is off (car is parked) it flashes. When the key is on, it goes out. I wired it using a bosch relay. If you do a search on this site for "Flashing LED" you should find some posts that describe in detail how to wire this and have a wiring diagram showing what terminal on the relay hooks to what.

Hope this helps.

p.s. I had no luck finding a suitable flashing relay on ebay or online. Look for a good local electrical supply store.

wire the resistor on the negative side of the bulb..................

Thanks Coppertop! Made some up this weekend and they work great!

Mark 66SS