Eric:

For automotive use you need to install special wires which keeps
specifications for this application. This single wires are specified as
"FLY" or "FLRY". Specification sheets will be found at
https://www.kbe-elektrotechnik.com/en/products/automotive-cables/

To run that wire below floor you need to cover it by a rubber or plastic
duct tube.

Helmut, '80 Vanagaudi