I have several large pumpkins on a vine but am not sure when to pick them.
I have heard they are similar to potatoes in that you wait till the vine starts to die before harvesting.
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Once the vine starts to die back, that is a useful indicator that they are ready or nearly ready.
Other indicators of a ripe pumpkin include:
If you leave a tomato on the vine too long, it may split, or a critter may come and eat it in the night. Pumpkins and their ilk don't suffer from either problem, so you can leave them as long as you want. The colour change is a big clue, but most people leave them until there is no chance of them growing any more.
In the late fall when we have a hard frost that leaves the ground white and "melts" a lot of tender foliage, it is very common to see bright orange pumpkins all over a field.
from http://photos.syracuse.com/post-standard/2012/10/pumpkin_harvest_at_abbott_farm_4.html - the grass and weeds between the pumpkins clearly weren't killed by the frost but the pumpkin stems and leaves were (look closely.)
If you are just dying to eat some pumpkin then tapping for hollowness and checking the hardness of the skin and stem are good things to do. But if you are just feeling a sense of nervousness that you should be harvesting now, relax. Take them in when the foliage is all dead and they are surely no longer growing.