Volkswagen Golf 4: Cigarette Lighter Relay Modification for Video Recorder - Issues & Solutions

Good day. In connection with the purchase of a video recorder, I decided to change the constant current in the lighter to one that will appear only after turning the key to avoid the battery discharge situation. After studying a few forum entries, I came to the conclusion that the easiest way would be to connect the relay to the cigarette lighter. The most suitable cable is the cigarette lighter backlight cable and I decided to use it. It should work on the principle that when the lights are turned on, electricity will appear in the lighter, causing the video recorder to start. Initially, I connected it as in the attached diagram, but replaced the 86 contact with the backlight cable instead of the ground. The solution works, unfortunately, when I turn on the lights, there is a hum in the relay. After starting the engine, the hum intensifies even more, it makes loud noises. I thought it was the fault of the 86 contact, so I connected ground directly to it. The effect is the same. A loud hum.
Relay is 12v dc A.
Overall a very good idea, but I don't know how I can remove this relay hum and what causes it. Can anyone help me?

Sorry, the autocorrect removed, the relay is 12v dc 30-40A

You have a good scheme and idea. And you have the option of replacing the relay because it is possible that it is faulty

Fly with the cable from the radio. There may be pulses in the backlight and so on. Alternatively, if you have to combine too far from the radio with an optocoupler or stabilization of this voltage.

From the radio, I also do not really have how to draw electricity because it also works on direct current, there is no need to turn the key. The only thing, when I was assembling the lighter housing, I noticed a yellow cable somewhere above, not connected to anything. Unfortunately, I did not have time to check what it is, the frost drove me home. Maybe someone knows if the color of the cable can mean something?

Yellow in the iso cube on the radio may be after ignition, but you need to check

And if not, then it will be a sure thing from under the fuse box

Check if the backlight is turned up to max with the potentiometer. But still the voltage after the "dimmer" is not suitable for a relay without stabilization / filtering.

Thanks for the hints. Unfortunately, due to the fact that I am studying in another city, I will be able to start it next or next Saturday. I'll try to fix it with that yellow cable, if it's after ignition, if I don't try to play something from the radio. The last resort will be a bypass from one of the fuses. As for this backlight cable, I actually forgot that there is a backlight potentiometer inside, I could at least check what was going on with the hum when turning it. The second thing is that there is something wrong with it because when adjusting the brightness of the backlight, it sometimes does not react proportionally to the shooting. The effect is the same as with a tarnished potentiometer in the amplifier. Maybe it is tarnished or dirty? I don't know, maybe he is the cause of the hum. Anyway, I'll try to do it with a different cable. Best wishes!

Test the relay coil under the battery and see if it buzzes. He should not. This way you will rule out a defect in the relay.