# How to connect headlight wires?



## rva1945 (Feb 11, 2016)

Hi:

Most of the two-function decoders include Function Positive Common, blue wire, besides function (headlight) wires.

I understand that the function wire goes to one of the light terminals and the blue (positive common) to the other light terminal.

Am I correct? Thanks.


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## Bwells (Mar 30, 2014)

Yes sir. White for headlight, yellow for backup light. Blue to both


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## rva1945 (Feb 11, 2016)

Thanks!


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## wvgca (Jan 21, 2013)

check the documentation for your decoder, three basic varieties for how much voltage is applied to lights .. some have a 1.5V, good for small incandescent, some newer ones have in the range of 3V, just right for white LED's, but most are full rectified track voltage in the range of 12 to 14V, for this voltage range you may need resistors depending on the type of light that you choose


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## rva1945 (Feb 11, 2016)

Thanks, a voltmeter should be the best choice here.


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## Mark R. (Jan 26, 2013)

A little known fact .... in some cases, I've had situations where it just wasn't easy to route the blue wire to the lights. In a pinch, you can utilize either rail (left or right) as the common to the lights. TCS used to include this wiring option in their documentation that came with their decoders.

This will provide half wave power to the lights - the voltage will be half of what the actual TRACK voltage is, so you will have to adjust your resistors accordingly.

Seeing as how you are using half wave common, the light is only receiving half the "AC" wave form off the rails. While it is a higher frequency than a typical AC power supply, some people claim they can see the pulsing when using LEDs .... that has not been my experience, and would be a moot point if using bulbs.

Mark.


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## rva1945 (Feb 11, 2016)

The flickering in the LEDs can be eliminated with a capacitor, provided a diode is included.


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## Bwells (Mar 30, 2014)

Oh my, do you know Ed?


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## Mark R. (Jan 26, 2013)

The capacitor should be in series with the LED, right ? :laugh:

Mark. (tongue planted firmly in cheek ....)


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## rva1945 (Feb 11, 2016)

No my friend, in parallel with it, and properly polarized.


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## rva1945 (Feb 11, 2016)

It was easy: it's 12V DC in the output when the loco is moving forwards. I should later give the yellow, rear light wire a try.

Thanks.


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## wvgca (Jan 21, 2013)

Mark R. said:


> The capacitor should be in series with the LED, right ? :laugh:
> 
> Mark. (tongue planted firmly in cheek ....)


ya sure, poke the Ed's-spurt bear  
[ you beat me to it  ]


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## wvgca (Jan 21, 2013)

rva1945 said:


> It was easy: it's 12V DC in the output when the loco is moving forwards. I should later give the yellow, rear light wire a try.
> 
> Thanks.



if one of the light functions is 12v, all should be as they share the same common power [blue]


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