Relais 109: Optimize Starting with Lighting

I've been experiencing the following problem for a few years now:

"When I start the engine without lights – whether it's cold or warm – the starter motor turns for about 3-5 seconds before the engine starts, but sometimes it cuts out again for 2-3 seconds afterwards."

"However, if I start the car with the lights on (any light), the engine starts immediately (within 1-2 seconds)."
I also always wait for the preheating indicator light to turn off before starting the engine. The difference is just whether the lights are on or off.

Apparently, the light switch is supposed to be causing this?

4) Apparently, there's a relay (model number 109) that was produced with defects and has been used in numerous vehicles (Audi, VW). It is said to have caused various problems, either consistently or intermittently. This information comes from the ÖAMTC (the Austrian equivalent of ADAC).

5) Relay 109 is supposed to be responsible for supplying power to the motor control unit.

6) Where can I find a wiring diagram? Where is the relay located? Is it actually called "109," and does it have a specific name?

Please provide the text you would like me to translate from German to English. I will then give you only the translation, without any explanations.

Thank you.
Robert.

Hello,
It would be advantageous to know exactly which vehicle it is, even just for having a wiring diagram.

Best regards, Richard.

"Sorry, how can I display my vehicle information in my profile?"
Data:
Model: Audi A4 8E/B6.
Body style: Sedan.
Year of construction: 2002.
Engine: 1.9 TDI Quattro.
MKB/GKB AVF ETQ GBC

Thank you for your help.

Robert.

Hello,

I am not aware of any such effect related to a light switch.
If it's reproducible, I would check if it also occurs when using a powerful external charger. If not, then the age of the starter battery becomes a question.

My wife's A3 also had some strange issues, ranging from ABS/ESP errors to starting problems. The AGM battery that was installed simply reached the end of its lifespan, and after replacing it with a new one, all the problems disappeared.

"An Autoscan feature would also be helpful."

109: No, it might also have a different name. The year of construction is a possible cause.

Best regards, Rainer.

Simply use the search function with "Relais 109 A4" .
Then there are some relevant results regarding the installation location, alternative names for the relay, etc.