My Cummins has one instead of glow plugs like many other diesels. IMO, i'm not sure it even needs it. I'm in Montana and even on the coldest days the thing could be sitting all night and it would fire in a few revolutions ignoring the preheat light with the modern high pressure common rail direct injection. Probably does help with cold emissions which might be why it is there still. There is a delete plate out there for those who want to ditch it.
