It's best to power the RPI separately, especially if you want to turn off the power supply.
A common GND must be present!
The Importance of Sharing Grounds
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1 and 2 +5V and GND to the power supply.
4 Data to RPI.
Depending on the number of LEDs, you have to apply +5V and GND to the strip several times.
6 and 7 is the connection from the back for +5V and Gnd.
regards pclin