LED wiring on a LT 4-8-2 headlight

[breezy8]

What is the proper way to wire a 3mm LED to the headlight on a LT MTN 4-8-2 It is now set up and runs on DCC. It has the board in the tender and I added w/ 8 pin plug a Sound traxx ECONOMI DECODER.  after so fiddleing, it runs great. .Now  I need to add a LED headlight...Thanks so much   breezy8

[breezy8]

I should clarify a bit. Both wires coming from the "light board" are black....which is the "RED" or +, and the other wire would still be the black or -.....I plan on using a 580 ohm resistor, but I need to know the polarity to correctly wire the LED......Thanks again..breezy8

[breezy8]

I should clarify a bit. Both wires coming from the "light board" are black....which is the "RED" or +, and the other wire would still be the black or -.....I plan on using a 580 ohm resistor, but I need to know the polarity to correctly wire the LED......Thanks again..breezy8

[breezy8]

Sorry about the double post....the site didn't show that the first had posted....sorry

[jbrock27]

LEDs have both an anode and cathode "leg" or side to them.  The cathode is the side connected to the larger of the 2 metal portions inside the lens  part. You may have to look with a magnifier to see this in the lens, but the wider plate is the one that connects to the cathode leg.  The other side, the anode, is the leg you want the resistor connected to and your + wire connect to.  Any questions just ask.  Good luck and have fun!  

If my words are not enough, here:

http://robotmill.com/2011/01/21/the-led/

[electrical whiz kid]

Jim;
So just for clarification, the unidentified (plain) leg is the lead to which you solder the resistor, correct?  Also, Breezy; do yourself a favour and install a "golden" (not yellow) LED.  For a headlight, a 580 Ohm might not be as bright as you ultimately would like.
Your locomotive, your cash, your call.

Rich C.

[jbrock27]

As described and identified above Rich, yes, the anode leg is the one the resistor gets soldered to followed by soldering the + wire to the resistor.

[brokenrail]

I think in order to tell witch one of the black wires coming off the board when they are both colored black can be determined with a volt meter.The meter I  have will show the negative voltage of the circuit if the red lead of the meter is touching it to test.Or you can put the resistor on either black wire then wile powered up touch the legs of the led to the wires and see witch way it lights .Since it will only light one way.Or use some small jumper wires with clips .
Johnny Adam

[jbrock27]

I like your meter idea; my meter has the same capabilities and that feature is verrrry helpful.  The beauty of a (good) digital meter.  
I may have misunderstood wheezy's question about polarity to be about the LED not the wires on his loco.  I am sorry if that was the case.  

I can also tell wires' polarity at times by where they are coming from, such as one side of the trucks or the other and which way the loco moves (nose forward or backward) when placed on the tracks in relation to which way the directional switch is thrown, in my case, on a DC power pack.