one more thing...
This may be a long shot:
I used to own an '81 diesel VW Rabbit, and I just remembered that it had a instant-block-type heater with a manual switch ion the dash. It also had a light that went off when it was ready to go. (5 minutes or so)
It was hooked up directly to the battery as opposed to having to plug it in.
Maybe check to see if you have a block or other type of heater installed?
Current: '91 300TE 4MATIC 317k and climbing...
'81 300TD Wagon 168K "Tank"
'83 240D 216K 4spd manual "Da Bear" (aka best car ever)
"Never sweat the petty things...
and never pet the sweaty things."