T-Vis Activator Wire?

Just to clear some things up here.

There is no such thing as "12V" LED... All LED's run pretty much on 1.5-2V. When you buy one from the store ready to go on 12V they have a resistor in series with it not for current limiting, but to act as a voltage drop. Typical LEDs draw about 20-30mA. High Intensity LEDs draw anywhere from 70-200mA. Either way, here is a little electronics lesson for everyone. So instead of spending 5 bucks on a "12V" LED, we can spend 50 cents on a LED and resisitor and make our own. This also applies to things like idiot lights, turn signals etc.(Examples are shown on the dash I made for my car)


OHMs Law

E
------
I | R

E=Voltage
I=Current in Amps
R=Resistance in Ohms

So we will take the average Car Electical system voltage 13.5V(This is debatable, but for these purposes we will use this.)

So we will need to know the current draw of the LED. For this example we will use 100mA. We know its operating voltage is 1.5V.

Ok. So to figure out the value of the series resistor. We need to calculated the voltage drop across the resistor.

_______Resistor ____LED //
+-------------/\/\/\/\---------->|-------To TVIS ECU Pin

13.5V ____Unknown V____1.5V

So far this is pretty basic. 13.5 -1.5V =12V


So now, we know that the voltage drop across the resitor is 12V. Now we know that the current is 100ma. This because in a series circuit the current is the same at all points.


So with that we do our calculations


12V
-------
100mA| R


R=12V/100mA

lets make this easier to work with by converting to Amps

R=12V/.1A

120 Ohms=12V/.1A

R=120 Ohms

So the value of your voltage drop resistor is 120 ohms.

________________ //
+--------/\/\/\/\/------->|-------- To ECU TVIS
13.5V___120Ohms___LED

Now for most cases a 1/4 -1/2W resistor will be fine.


The only issues I would stress about tapping directly into the ECU for control of the resistor is that the transistor inside of the ECU may only be designed to handle so much current. So use caution with how much extra current draw you put on it that TVIS lead as you may burn out the ECU.


By the way the pinouts for most typical LEDs is as follows.

The Anode is Positive which will be the longer lead
The Cathode is negatibve and is the shorter lead and usually is denoted with the flat side as well.

-------->|-----
Anode Cathode


Ok so now go down to radioshack and spend less than a buck and have fun.

Heres a link on everything youd every want to know about LED's

http://en.wikipedia.org/wiki/Light-emitting_diode