So I went ahead and took the radio out and confirmed that it is indeed MOST by the fiber optic cables. In fact, all the wires and connections are exactly the same as on a E9x.
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[Current] Tesla Model 3 Performance
[Retired] Audi R8 V10 6MT, BMW i3 BEV, BMW i3 REx, BMW Z4 sDrive35i DCT, BMW 335i Coupe 6MT