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Discussion Starter #1
So I got this 20 pack of lights with resistors installed. They are prewired for 12/16V DC. So I try to test them on my little Tyco power pack with the DC throttle terminals and get nothing. Just for kicks, I touch the AC accessory terminals and they work! So what's going on? Why not DC working the lights?
Thanks
 

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Yard Master & Research
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On DC they are polar sensitive. You should of switch leads. AC they work on half wavelength. Polarity does not matter .
Be careful with Tyco some transformers put out 20 volts. Can't remember if it was AC or DC.
 

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Discussion Starter #3
Thanks, T Man. I reversed the touch on the wires on the DC terminals and it's fine. Never thought to do that! :)
 

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I've bought several LED sizes with the diodes pre-installed.
On all that I've bought, the red wire is the "+", "common" lead.
The black wire is the "-", "switched" lead.

An easy way to test them is to use a rectangular 9volt battery...
 

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What you have are LEDs, not light bulbs...

LED stands for "light-emitting diode".

A diode is an electronic component that only lets current flow in ONE DIRECTION. (It's basically a one-way valve for electricity.)

So it has to be supplied DC (directly current) power in the correct polarity in order for current to flow through it and light up. If the polarity is wrong, the diode prevents current from flowing "backwards" through the device.

On AC (alternating current) power the polarity is alternating back and forth at 60 times per second, so the LED is actually continually turning on and off as the power reverses itself, but it's so fast your eyes are not capable of seeing it and you just see it lit up.
 
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