This is my first winter driving this '83 TD. Unfortunately, things aren't going well. I'm in Michigan and we're talking about 0 degree temps at night (and sometimes during the day) for quite a few days now.

Current situation:

Car won't start, even using an external battery starter.
Glow plug light on dash comes on and I hear the "click"
Oil pressure is good
-- not able to do diagnostics beyond that right now b/c it's dead in my driveway

Over the past few weeks, the car has been getting progressively harder to start in the the cold weather.

Earlier in the week, the car started after about 10 minutes of cranking, while attached to the external battery charger but now even this doesn't work.

Suggestions on where to start checking, or what to do at this point? Thanks. I know I didn't give much information, so I'll try to clarify or test things if people ask questions.