I have my 3DR radio plugged in to telem1 port of Pixhawk and it is flashing green.
I have the other 3DR receiver plugged direct to laptop USB and driver is loaded. On mission planner I selected com6 57600 baud, when I press connect it always times out and never connects?
mark
Hey, I assume you have already uploaded firmware onto your pixhawk?
However if the LED is flashing green it means its not linking to the other module, so my suggestion would be to connect both radio modules to your PC and make sure they have both got the same netID settings on them.
If they are both connected the green LED should be solid and the red LED will be flashing indicating data I being sent/received.
If you need anymore help just let me know 
here are my steps:
pixhawk firmware is installed.
pixhawk is powered on, 433 mhz xmtr is connected to Telem 1 port.
it is flashing green and transmit red light is pulsing.
I plugged in the 433 mhz radio rcvr straight into my Win 7 pc with NO adapter cable. i can see the driver installed on my pc as:silicon labs cp210x com6, 57.6kb.when i go to mission planner and use the same com settings i does not connect.can you offer any advice?
thanks buddy!