Power Injection: Power injection means running 2 extra wires from the power supply, and connecting them to the + and – wires on the LED strings at one or more places. Here are a couple examples: If the power supply is at one end of the Run of LEDs you can connect the extra power injection wires to the power supply and run them parallel to the LEDs and even put them in the channel with the LEDs. Then at one or more places you splice the +/- wires from the LEDs and connect them to your power injection wires. The power injection wires don’t have to run parallel to the LEDs. Let’s say your power supply is located in your attic (which by the way is an excellent way to keep it out of the elements and make it easy to access in the future). You can run pairs of wire from the PS to several points along the String of LEDs. Maybe you connect in the middle and at both ends. In fact, connecting power to your strip in the middle is a good way to reduce voltage drop. Remember the power (+/-) doesn’t have to start at the beginning of the string. The electricity doesn’t travel in just one direction. So connect it to whatever part of the string is easiest or makes the most sense for your situation. However, the Data Signal DOES need to start at the beginning, but the power wires don’t. Power injection doesn’t involve the data wire at all, just leave that wire alone. Why might you need power injection: First point is you only MIGHT need it. You also might NOT need it. In General, if you’re using 12v Pixels you won’t need power injection until you get to about 250 Pixels. Even if you DO have more than 250 Pixels you might not need power injection if you keep the brightness down. That’s for 12v LEDs, 5v LEDs on the other hand need more power injection. If you’re using 5v LEDs, you’ll probably need power injection if your strip has more than 150 LEDs. Now, if you’re not sure if you need power injection, you could connect all the LEDs, turn them on and check for dimming. If you notice your colors look dim or just off as you get to the end of the run, then you need power injection. If you can live with the LEDs being a little less than full brightness you can try turning down the brightness until the dimming and color changes go away. Or just give in and do some power injection. Be really careful that you don’t mix up the +/-. Most LEDs will be destroyed if you accidentally swap the + and -. Data Signal: The data signal comes from the controller. It’s what tells the LEDs what colors to be and when to blink, fade or whatever. There are a few rules to remember about the data signal. It has to travel in the correct direction. All these LEDs will have some way to indicate the direction the data signal needs to travel. Different companies mark it in different ways. Sometimes an Arrow, sometimes letters like DI. If you’re unlucky and your LEDs don’t have any indicator then usually the female connector is the beginning of the string. If all else fails you can try connecting the data signal to either end to see which is the beginning of the string. It won’t hurt the LEDs to connect the Data signal to the wrong end. Data Signal needs Strength: When the data signal starts at the Brain of the controller it comes out at 3v, but the LEDs are generally expecting 5v. That is usually fine unless the data signal voltage drops any lower. What might drop the data signal voltage? A wire that is too thin or too long. So what do you do? The best thing to do is boost that voltage signal to 5v. There are a few ways to do that. The easiest, is to get a controller that is made to boost the signal. Like the DigUno or DigQuad. You can build your own, or you can buy them pre-assembled. I’ll bet you can guess where to find the links. But, if you don’t want to spend the money for those then you can use what the pros call a Sacrificial Pixel. Sacrificial Pixel: when the data signal hits the first pixel in the string it is bumped up to 5v (yes, that’s true even with 12v Pixels). So after that first pixel the distance between the first pixel and the rest of the string can be really really far. I tested it and got as far as 40 meters of 20g wire before the signal started to degrade enough to get flickering. The last thing I’ll say about the data signal is that it can be split. You would do this only if you want all the lights to do the exact same thing all the time. To split it, you just splice in a wire and run it to a new string of LEDs. You can split the data signal anywhere along the string. Those LEDs should also be powered by the same power supply.