Car won't start, lights not working

I have a 1994 Volkswagen Golf III 1.6L gasoline engine that won't start and is currently at the repair shop. The starter switch has already been checked, and all the fuses in the car are fine.

If the warning light on the driver's side turns off when unlocking the car, the immobilizer should actually be deactivated. However, due to the electrical fault, I can't access the control unit to check it.

Does anyone have a tip for me?

Sure, here is the translation of the text from German to English:

"Hello"

We once had a 1996 Passat with almost the same symptoms.
No warning lights illuminated, the vehicle wouldn't start, and due to a lack of power to terminal 15, no communication could be established with the control unit. Additionally, the alarm system indicator was flashing erratically and triggering alarms intermittently, even though it was supposedly deactivated. The vehicle could be unlocked, but the alarm indicator continued to flash in some cases.

After a long search, it turned out to be the door handle on the passenger side.
Simply disconnect the connector on the passenger door > A-pillar, and everything started working again (ignition, diagnostics, engine start) - then the door handle was replaced.

@vagtuning

I have a slight lack of clarity in understanding.
What exactly is the purpose of the door handle on the passenger side? Does it trigger the alarm system if the handle is activated while the door is closed? And why does the car fail to start when the handle malfunctions?

'There's something strange with the old Passat. When you briefly interrupt the power supply, the central locking system goes crazy. The DWA (alarm system) doesn't indicate that it should turn off, and then the WFS (window lifter system) doesn't allow it to turn off either, because as long as the DWA is active, the WFS doesn't receive power on terminal 15.'

Hello,

I recently had the same problem. In my case, it was the alarm system/immobilizer.
Control unit is not diagnosable.

Installation location: somewhere behind the distribution box insert.
Sometimes, just a few well-aimed hits on the black box are enough.

Best regards,
David