in need of instructions for radio

We lost the function of our radio in our 1992 525i due to loss of power. We bought the car used and it did not come with a radio manual. We know that the car was brought to the states by the original owner who was in the military. We are told we have a "european" radio - unlike anything the mechanics around here have seen. They are used to a 5 digit code and ours is only four digit - I believe we have the code but not the instructions on the sequence in which to re-activate the radio. Can anyone help with the instructions or tell me where I can get a hold of a replacement manual?