After serious thinking Pete Verdon wrote :
I would say yes. Treat the whole car as an appliance - it has a metal case
and can't be certified as double insulated, so the case must be earthed.

Things get more complex for a boat, where galvanic corrosion in salt water
needs to be considered, but for a car I'd certainly connect the body to the
earth in the connector.

No one has suggested an earth rod )

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk