AAZ: Preheating via Turbocharger Contact

Hi!
I'm having a problem with a 1.9 TD AAZ engine from a 1993 Golf 3.

Prerequisite:
The glow plug system seems to be working fine overall, all fuses are okay, and it pre-glows properly when the ignition key is turned to position 15.

Problem:
Specifically, the preheating system should start heating as soon as the driver's door is opened and then closed. However, it's not doing that! I've done some experimenting and found the following:
If I disconnect the glow plug timer (marked with "120") and then reconnect it, the preheating function works exactly once via the door lock. After that, it doesn't work anymore, even if I start the engine or do anything else in between.
If I also completely disconnect the coolant temperature sensor (effectively simulating Arctic conditions), the preheating function works exactly twice via the door control. This is perfectly reproducible!
So, the question for me is, why do I always have to subtract the warm-up time?
Door contact switches, fuses, spark plugs, and coolant temperature sensors should, in theory, be okay.
How is the device reset so that it doesn't preheat every time the door is opened (e.g., when vacuuming or cleaning)? Is it disconnected from the power supply somewhere, or does it receive a signal somewhere? Pinouts with cable colors would be great!

Thank you.
Dirk.

Hi,

I've also driven an AAZ before. As far as I know, the AAZ only glows once when you open the door. If the engine doesn't start, it won't glow again the next time you open or close the door.

Even when the engine is at operating temperature, the preheating function doesn't work through the door contact.