How does this radio ground?

[6670charger]

How does this radio ground?

I will be buying a 92 525i Wagon in a few days. This is a European spec car and located in Germany. The car has no radio in it right now, but, I found and purchased a factory radio and its wiring harness plugs from a junked similar vintage 7 series car. I assume most of these radios interchanged in some fashion, and that all I have to do to hook it up is splice the matching wire colors in the dash to the wires to the plugs for the radio.

My question is, how does this radio ground? Does the threaded stud in the middle of the radio (rear view) ground to the body? There doesn't seem to be a specific ground wire, unless the Germans use a color other than black to designate ground.

I've attached a few pics of the radio front and back to help show what I mean.

Any suggestions would be helpful.

Thanks.

[tim eh?]

ground is the big brown wire.
powered are red and violet/white
remote signal (so amp turns on) is white
speakers yellow and blue

the stereo system is complicated it works with an amplifier in the trunk and it might have an external F/R fading system you should definitely try to read up on this i don't know what was in the 7s.

+ it is different in europe from here maybe you don't have the amp ... ?

[6670charger]

Not sure if I have the amp either. Guess I'll have to wait and see what, if anything, is in the cargo area or hidden in a compartment back there.

Thanks.

[BMWDriver]

The amp should be in the left side of the trunk, behind the "carpet" wall, mounted on a metal frame that you will see before you can notice the amp. I had fun taking mine apart to use some of the parts to make a filter to match up to my updated head unit.

[6670charger]

Hey, thanks! At least I know where to look in the event there's a problem. Are there two different amps, one for the antenna and one for the radio itself? Was doing some looking on ebay in the event I have to replace it for some reason, and found two different parts under radio amp. One was a small metal piece with some connection points on it, and the other was a larger black box similar in size to a CD changer.

I'm going to assume for now that the amp works and that the radio was just taken out by a previous owner and put into another car. Many, if not most of the older cars over here had the stock radios removed and replaced with aftermarket ones that will play CDs or MP3s. The owners seem to pull the radio before selling the car. I'm only here for a short time and haven't wanted to spend much over $1000 for a vehicle. Can't begin to tell you how many used cars of all Makes from this basic vintage that I've found for sale with no radio in them. Can't possibly be because all these radios have failed.