When the Rover Group were under control of BMW, they set about getting a new model to launch the new company and they came up with the Rover 75, they raided theyre parts bins from the range 3, 5 and 7 Series), they also used the very good derv engine, they mated all the bits into a BMW/Rover designed shell, that is why the Rover 75 is a very good car.
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The ZS has bits of BMW in it too, the Wiring loom is full of BMW connectors, but mostly you will find Honda as the main supplier of bits.