When you open the rear hatch, the cargo light comes on then as the hatch continues to raise up and you remove your hand from the hatch handle, the cargo light sometimes goes out. Where is the switch that turns on the rear cargo light? It probably needs to be WD-40'd. It isn't located in the door jamb like the other doors are.

I think it's down where the latch is. Look down there for it.

When I read your entry I didn't immediately think that you had a bad switch, but rather a break in the wires that go from the body of the car into the hatch. Could it be that as the tailgate goes up, the wires stretch in the corrugated rubber boot, and the broken wire breaks contact, only to reconnect again as the tailgate goes down? Just a guess.

I think it's down where the latch is. Look down there for it.

 

I discovered the hatch switch is incorporated into the latch and it needed to be lubricated. Problem solved. Thanks.