Fake alarm led light, need help

**MidnightSXT** · 10-01-2007, 03:30 AM

I`m too cheap to buy an actual alarm, but they say a visual deterrent such as a flashing light will most likely fright off a thief...they move onto the next vehicle with no visuals. Anyways quite some time ago I bought a varad blue flashing hyper LED and had it wired into my old chrysler 5th avenue(before I bought the magnum). I followed the wiring instructions and it worked in this car no problems. I had it wired this way, so that the light would flash ONLY when ignition is off, and goes off when ignition is on.One wire gets hooked up to a constant 12v source and two other wires get twisted together and run to a source of ground that is ONLY ground when ignition is off. This would be any ignition switch 12v powered accessory. This is because when the key is off,anything thats key powered automatically becomes a source back to ground. Well this is the problem i`m having with the magnum. In the Magnum I mounted the LED inside the rear view mirror so it flashes towards the front of the car. Here is what I did. Powered the LED from the 12v "fulltime" power wire that illuminates the roof console map lights. As for a switched ground I used the cigarette lighter, and yes I know about the 12v constant/12v switched trick with the fuse. Mines set to 12v switched. (here is where that key off/12v switched wire now becomes a ground source comes into play.) I confirmed all my 12v and ground sources with a digital meter. Now with key on the LED goes off as it should. Key off the LED will flicker dimly but very rapidly after the door is opened then shut, then resume a normal slow steady very bright flash once the interior light delay has shut off the interior lights. The LED will now continue to flash in this normal bright pattern for roughly 2 minutes and then all of a sudden it dims out and hyper flashes the same way it did when the interior lights were on. This is where i`m confused. I`m thinking its almost like my 12v constant source drops full 12 volts after a couple minutes, or either that my 12v ignition wire loses ground after a couple minutes, OR something in the module that controls interior lights doesnt like its "new found LED friend". I should add that when I turn the interior light dimmer switch on the headlight switch to the all the way off position, I dont have this hyper blinking dim LED problem when the door is opened then shut. Anyone have any ideas on what the problem is? One way I could rule out my 12v constant source as being the culprit(keeping in mind this is strictly for testing purpose only) is simply wire the LED right to the battery positive post and keep my cigarette lighter switched ground wire as the ground. If I get no problems then its obviously a 12v constant source problem/light module problem. If I do get the dim hyper blink led with this test then it HAS to be my keyed ground. And if thats it then i`m kinda screwed for a keyed ground as I feel no matter where I ground it to a keyed source, i`d still have this problem. My last resort is to simply wire the LED to the battery with a fuse, then to a tiny toggle switch hidden somewhere then ground right to body. I have a feeling there is even a module that controls body grounds unlike old school 12v wiring where everything was grounded right to a piece of metal attached to the body. So anyone have an idea.....other than buy an actual alarm lol

**elcobra44** · 10-01-2007, 01:03 PM

It's just a matter of time before I do this myself..

I would try a different power source and one that isn't connected to the lights. I'd use the cig lighter for that and switch the fuse so it's hot when the car is off. Then relocate the ground wire to the ignition wire inside the dash.. I think it's pink/white?

Guest · 10-01-2007, 01:06 PM

Be careful as our cars don't take to battery drain well.

I used to plug my radar detector into my center console and leave it on all the time. When in my garage it never goes off, but has one single green LED as a power indicator.

If the car sat for more than 2 days the battery would die. It happened 3 times in one month.

When I took it to be checked they tore the car apart only to discover the radar detector was the source of my issues all along.

I now plug it into my ashtray lighter that turns off with my ignition.

**elcobra44** · 10-01-2007, 01:09 PM

A single LED isn't going to draw nearly as much as a radar detector, but to be on the safe side, I would still add a hidden switch for it in case you plan on not using the car for a long period of time.

**JamminWagon** · 10-01-2007, 11:15 PM

The map lights are like the interior lights will shut off after a few min after the key is removed and the doors are opened. You can confirm this by sitting in the car until the LED stops flashing and testing the "full time" power tap.

I am using the cig for switched and the left over canbus connect left over from when I upgraded the stereo for contant, but i have a constant ground. The unit I have is a lil circuit board wrapped in plastic. I paid $10 for it at a local stereo shop.

I have let the car sit for 10 days at a stretch without killing the battery, as stated before the LED draws so little power that it will take a long time to kill the battery just from the LED.

**MidnightSXT** · 10-08-2007, 06:39 AM

My follow up to this semi-dead topic. Found my problem. My cigarette lighter switched ground source wasnt the problem.The 12v tap at the console lights were. After digital meter probing the hot wire and the meter grounded showed me that I had 12v when the console lights were on or a door opened then closed. This 12v dropped down to no more than 4 volts after 30 seconds or so. But once either a door was opened or the map light itself were manually pressed the voltage upped back to 12. Ok problem solved. I left the ground where it is and tapped into the unused constant 12v source for where the clock goes in a 300. I test probed this positive wire for a couple minutes and determined this is a good non fading 12 volt source.

**silversteelsrt8** · 10-09-2007, 11:44 PM

so you are able to get your fake led light to work once you close the door it will start blinking

**SmoovC** · 10-09-2007, 11:54 PM

Simple solution:

Using a 12 volt flashing LED:

Hook the positive LED wire to constant 12 volts; light blue with red stripe at the back of the key cylinder.

Hook the negative LED wire to ignition; pink with a white stripe at the back of the key cylinder.

Since ignition reads ground when not energized, the LED will only flash when the car is not running.

Hope this helps.

Chris