Shame British (not EU) governmental policy has left us with very limited indiginous car manufacturing.
Sure, we assemble, sure, we build... but just about everything left is owned by somebody external to the UK.
That in itself (a consequence of British, not EU policy) makes us more dependent on the EU and other partnerships then we had any need to be.
In a funny sort of way it might not. As a lot of manufacturers in the UK trade with Europe most material purchases are made in Euros.
If the pound actually declined as forecasted our manufacturing base would undoubtably profit.
Regarding cars specifically if I'm honest I would be surprised if exports were damaged. Certainly net influx of cars into the country far exceed exports to Europe. Not only that but most brands, especially the luxury German ones, make more profit per sale here than mainland Europe,
I'm not being a berexit madman here but just pointing out that is really don't think manufacturing would be harmed. A strong pound is not great for exports.