So, trying to be a little more helpful, here are a couple of photos of my TA 4x4 behind the glove box (which has been removed). The silver box in the photos is connected to the radio head unit and, from memory, is described as the radio module. This seemed to be some intermediate connection between the radio and BCM. I am guessing that you need this to match your replacement radio??
@AndyRKett seems better informed on the FIAT electronics and may be able to help?
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I have, in the past, had to have the BCM reprogrammed to accept a couple of new key remotes. I found an independent auto electrician that had the gear to do this (rather than a FIAT main agent who wanted silly money) and i suspect they would be able to do the radio too. However, it's not the job for a "regular" auto electrician - I had to ask a lot before I found one that knew FIAT and understood the requirements - oh and I ended up driving 200mile round trip to get it sorted!