My driver-side pigtail is toast. I did trouble shoot with an Ohmmeter and Voltmeter which told me the main line (positive terminal, low-beam) is fried. Both the high beam and common ground still work but the entire pigtail is so corroded I fear they won't last much longer either. But when I opened up unit to change the pigtail I find a major problem. The pigtail I purchased is much MUCH different than the one already on the car (the same unit is mounted on both sides.) Now, when the dealership looked at the headlight system they claim those are the correct units, and that the ones I bought are from '86 on. However the source I purchased the unit from AND my service catalogs claim that this new one is the correct model. Which is correct? I really don’t' want to trust the dealership for several reasons, the largest being the pigtail connector itself says VW!
Does anyone know which is the unit I need?

The pigtail I purchased:


The existing pigtail (The white plastic unit was removed
a while ago for rewireing nmad is exactly the same):


Issue:

 

I do not know the answer to your question. I do know two things (actually I know quite a bit more - but only two things are relevant to this discussion). First, there are a large number of VW and Audi parts on the 944 series cars. And second, there is no such thing as a model year change over at Porsche (this is a bit of an exaggeration, but stick with me here). It is known that Porsche will switch to a "new" part if they run out of the old part "without" waiting for a model year change over (hence the 85.5 interior). As such, the part you have purchased "may" be correct but still not match what you have. I would suggest that the best course of action is to modify your car to match which ever part is more readily available.