First ensure you are getting a good connection by twisting in both locations and push the connector in and out a few times.
I found the connection at the 4300 needed some 'working in'.
Makes sure the 4300 power button is ON all the time (pressed in).
With the trigger cable disconnected from the 4300 turn the 950 on with the green button, or remote (the power switch at the rear panel should always be ON) you should read 12 volts on the plug. The center tip will be positive (+)