wiring for w123 stereos

[JHZR2]

Hello,

my 85 w123 has a becker grand prix. I have a becker europa that I am getting refurbished by becker, and will install it in my car (it was from my 83 123).

My question is, which color wire do I attach to each spot on the radio? speaker wires make sense, antenna wire makes sense... but there is brown, black, red, and grey... more wires than i have spots for.

I assume that red is hot, and brown is ground to the bolt on the back. but the black??? I think grey would be for 'illumination' of the grand prix - not necessary on a europa.

Any info would be appreciated.

Thanks!

JMH