I just added a basslink to the other day, so I was doing the research on the board. While I wasn't specifically paying attention with regards to non-US Cars, iirc, there was a post that said the amp in the UK cars was under the spare tire.

I can't confirm this in anyway, but it's worth a look.

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Matt Atkins
'01 Titanium Silver X5 4.4
'01 Lemans Blue M5