300SL Security System LED Add-on

[hifeverz]

RE: '90 300SL

I would like to add a flashing red LED on the dash or console when then the doors are locked. Has anyone added one to the existing security system?? And if so, where and how would this be wired to??? Voltage capacity of the LED would have to be 12v???

Thanks,
HZ

[LeaUK]

Hi HZ

LEDs are typically rated between 2.5V and 3.8V (3.5V for blue) and therefore you will need a resistor is series with the supply. This can be calculated as follows:

R = (Supply Voltage - Forward Voltage of LED)/LED current.

Therefore:

For vehicle running = 13.8V
Blue LED - Vf = 3.5V
LED forward current (typical) = 15mA


(13.8-3.5)/15E-3 (15mA) = 680ohms


But you can buy flashing LEDS with integral resistor preassembled. However you will need to interface it with your ignition somehow.

For my car I have a CAT II immobiliser which happens to have a red LED (which is about to be changed to purple) that flashes accordingly

Hope this helps a little

Lea

[hifeverz]

RE: 300SL Security LED Addition Concept.

I do have a 12v flashing LED (resistor built-in) and I have attempted to try installing one in a Delorean have an existing Hofco Alarm System. I was unsuccessful after an hour of attempts at the various ignition poles, alarm brain contacts, ignition off and alarm armed. I was only able to bother my neighbor after repeatedly tripping the alarm siren in my quest for success.

I was hoping that someone has done an add-on already to avoid over exertion on my part. If anyone has any additional hints to try out, I will proceed to locate a contact in the ignition cluster that is powered when ignition is turned off and NO POWER when ignition is on. Are we confused already??

Any enlightment would be appreciated.

Thanks,
Hz

[bobterry99]

If you don't find a source of twelve volts which switches on with the ignition off, then you might consider the circuit below. The transistor is a PNP bipolar-type and the value of the value of the resistor can be about 10K to 50K. All parts can be readily had from Radio Shack for two or three bucks.

[hifeverz]

Thanks [bobterry99] for the schematic . . . I'll put components together and post the results.

I'll also get that 3.5v LED, in another color other than red + the 680 ohm resister to install in the dash. [Thanks for the idea Learoy]

A wealth of info. and appreciation to all at this forum.


Hz