Generally, use which when the clause that follows is not crucial to the sentence:
The information about the fridge being red has been added "by the way."My new refridgerator, which is red, has a wine cooler.
The information that follows that is essential to the understanding of the sentence.Thus it is true that these dialect preserve some English forms
You will usually use which after a comer.
Of course, there is a gray area where you can go either way.