Hi,

It is really simple. The BM came in 2 versions

BM54 Back = OG connector (round pins)
BM54 = NG connector (flat pins)

You can buy an adapterharness from OG cable to NG-radio BM54 but not the other way. The latter doesn't exist or you have to make it yourself.

The BM54 Back radiomodule is actualy a BM24 in a new housing (just the antenna leads are different, it has the NG-antenna connector). Biggest difference in the BM54Back and the BM54 is the possibility to connect an AUX-in port. The BM54 Back never has an aux-in possibility. The BM54 has it from a certain production week in 2002.

Roland