05 volvo 780 isx - strange electrical issue

So today pulled up to us customs booth turned off the truck, engine shuts down everything is normal but when I looked at the dash it was light up and heater fan was going. Took the key out no change. Turned the ignition back on but not starting and then off everything went off. Had to go in to customs and turned off the truck but dash stayed on even with the key out. Went to the buffalo dealer electrical expert thinks it a power relay so pulled P2 dash and fan goes off. Put new on in and still have the issue. Everything works on the truck as normal but to get the dash and fan off have to remove p2. Any ideas , where to start? Thanks