I got a couple of assumptions wrong about which colours were which pins, I just found a generic data sheet.
I think the LEDs are connected like this:
To confirm this you can do the following checks:
Connections should exist between:
Pin 2 and Pin 11
Pin 8 and Pin 17
Pin 1 and Pin 10
Pin 7 and Pin 16
Pin 3 and Pin 12
Pin 9 and Pin 18
When you connect 3V to resistor 331 this lights red on the final LED, as the resistor is in the posistion shown in the picture.
When you connect 3V to resistor 271 this lights green on the final LED as it has the same configuration as the Red strip.
When you connect 3V to resistor 151 blue does not light, as this resistor is before two LEDs, and 3V is not enough for both voltage drops. Try something more like 5 or 6V and blue should light on two LEDs.
if I put gnd on pin 4 and power on the second half E of the connector light up blu led of the first led
if I put gnd on pin 11 and power on the second half B of the connector light up red led of the first led
if I put gnd on pin 3 and power on pin D on the first half of the connector light up green led of first led
This would suggest applying:
Power to second half E controls blue on all 3 LEDs
Power to second half B controls Red on all 3 LEDs
Power to first half D controls Green on all 3 LEDs
Just 3V isn't enough to power them as the 3 LEDs are in series, 6V or more depending on the voltage drops of the colours.
Red is usually ~1.7V
Green is ~2.0V
and Blue can be up to ~3V.
if I put ground ( with gnd on GROUND bigger pin of the connector ) and power on pin 11, both second and third led light up red gentle not bright
This is because you are connecting power through 2 of the LED's in the red chain, and 3V is probably about enough to get the dim glow from 2 LEDs in series (Due to the 1.7V drop - 2x1.7V isnt too much more than 3)
My final assumption would be that the 6 remaining lines pass through this 3 LED strip and into the next strip... so the LED's down the 5m strip are controlled in groups of 3.
So 3 of the 6 unused input pins pass to the 3 colour inputs of the next strip, the next unused set of 3 shift down a set, and the current input gets shifted to the top of the pile. I am struggling to explain this, I will try a diagram.
http://www.obr-recording.co.uk/Arduino/RGB Strip 2.png