Thanks for bringing this up, I need to read about this. Is this what you would call an afterglow kit? Does the stock setup turn off the glowplugs when you hit the starter?

This article calls it "post-glow". From that article I am guessing that our old systems do in fact turn off the glow plugs when the key is turned to the on position.

This thread is a good read on the subject:

Glow plug Relay Upgrade