Power Injection ws2811

Hello all
I have installed set of 220 pixel lights on my house. I have a 350 watt power supply. The lights are 12v and losses colour and brightness from the middle of the maybe the 60th pixel. The problem is that when ever i try to inject power at any point in the whole string it shuts of the the entire lights . I checked with a multi meter and power supply voltage is good. Using a t- joint 3 pin power injection cable with 18awg wire. Anyone can help me out here.

Are you injecting power from the same power supply that is powering the beginning part of your lights or from a separate one?

Check the pins on the T connector with a multimeter to make sure you are using the right ones +/- for injection.

if you are using a new psu make sure all the grounds for everything including the microcontroller are connected.