BC LCD: Poor Visibility & More Combo Issues

Hi!

I bought a Volkswagen Golf 4 TDI 74kW PD, model Pacific, manufactured in 2003, about 3 weeks ago.
I learned from the previous owner that the car was involved in a minor accident on the left side.

After 3 weeks, I'm noticing some defects that I want to fix.
First, I had to have the voltage regulator on the generator replaced because it wasn't working.

The middle LCD screen on the AI unit is difficult to read, even with the blue backlighting.

The LCD backlight is sometimes good and sometimes better. I think it's due to the light sensor located near the speedometer, because when I shine a flashlight on it, the LCD becomes brighter, and it gets darker when I remove the flashlight.

I also noticed that a blue wire runs from the blue connector on the KI unit to terminal 12 (for the generator). I suspect the previous owner may have tried to hide this issue using this method, but I still need to check where that wire leads.
The display looks like this:



Then I also had problems with the fuel gauge (the display on the instrument cluster is not accurate). I noticed that the float had come loose from the diesel pump housing inside the tank. After the repair, it's not much better. After a full tank and about 200 km, the gauge is still showing full. (It also took about 20 minutes for it to go from 0 to full).

p.s. Could it be that the AI is malfunctioning?

P.S. I'm from Slovenia, and I apologize for any typos!

If you bought it from the dealer, it's their problem. They should install a new control unit for you. This issue also affects Audis manufactured up to the year 2000. In those cases, it's often a temperature problem or poor solder connections on the light sensor or the brightness control.

I bought it privately!
I already bought another AI unit on eBay, and I'm going to try swapping the sensor and LCD to see if it makes a difference!

I can also exchange the AI module, but I still need the 4-digit PIN code for this AI module and a new AI module to reprogram it. Is that correct? I think it's a WFS III immobilizer.

Best regards.

You need the Vehicle Identification Number (VIN) of the car in which the AI unit was installed. The LCD cannot be replaced; it's a permanently soldered-in film. You might be able to replace the light sensor if you can solder SMD components and have the necessary equipment.

I already have the 4-digit login code for some new AIs, but I haven't received the 4-digit login code for my current AI yet!
I have SMD technology equipment, including a hot air station and a fine soldering iron.

Best regards!

I have another question: Where is the brightness control? Also, I would like to exchange it if possible!
Is there a wiring diagram or service manual available for VDO KIs (engine control units)?

It should be mentioned in the manual. On my A4, the left pin on the instrument cluster is a rotary knob for adjusting the brightness.

Okay, in the Golf 4, it's on the left side, near the light switch! But the rotary knob for the lighting is fine, so I won't be replacing that!
(I thought there might be another light controller on the AI PCB.)