I want to install a Becker grand prix 2000 stereo into my 1983 500 SL,
but the wiring for the radio is a bit confusing to me:

blue + brown + brown + green/red wires together

red and grey wires together

Can anyone tell me what's this all about - the car is equipped with a
power antenna.

Regards, Werner

The blue is for power antenna.

The brown is for ground... but you said you got two of them?

There is supposed to be two power... one is always constant power 12V and
one of them power on only when ignition is on. You will have to use
voltmeter/multimeter to figure this out.

Then you have speaker wires... each has ground and positive so in SL, you
probably got only two speakers... so that is 4 wires.

I believe the grey wire is for light... it gives you 12V When you turn on
your headlights. so you can see your radio at night.