Yes, there are a few conditions that needs to be met before the valve to the main tank will open. It must have enough space in main tank. If the car is at to much of an angle the valve won't open. You can find this info in your manual.
You don't hear any defenit noise to indicate transfer. Al that indicates is the light on the switch. And the transfer is sloww. The first time I used mine I thought it was broken. Then after about 10min. I saw the main tank level responding. It takes a good 30k's driviving to allow enough time for the the sub tank to empty itself.
I got my Patrol this year through NissanSA and it has a sub tank (35liter) main tank (90liter) it has 2 seperate filling places. 2 gauges in the instrument cluster. This is standard on patrol as far as I know.
Problem I'm having is that the car run out of diesel on a qauter tank. At just above qauter she dies. Ad feul and of you go. This wil hopefully be sorted via nissan early in the new year.
Being alive is a Blessing!!