I need some help please. I bought a e30 325i 1991 Cabriolet and just in the process of restoring bits. There use to be a telephone installed once upon a time. I picked up an old brick telephone from ebay and its originally from a 1999 750iL. My friend an auto electrician has had a look at it
we trying to put together to make it work somehow, His asking me for a wiring diagram where we can understand the individual wire colours and correct harness to use. I understand signals went out on some of these some time ago and GSM is dying out but I thought it be good to have it linked up 
. I appreciate any help, diagram, connectors, or instructions please. Many thanks. https://ibb.co/ZJMn693
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