12v 400 amp cable size for winch or two cables instead of one
I don't have the current capacity for the cable you quote, but I fitted an electric winch to an HGV tractor and trailer a long time ago. If your cable is under or close to 400A then running two in parallel will work as well. If you have not bought the cable yet - then go up to 600A...

I used flexible 600A welding cable (this is only 1/2" or 5/8" diameter from memory) and soldered the lugs both ends. The idea was that the cable was stored clamped / fixed to the tractor unit 24v battery cover, then once the trailer was in position the cable could be connected to the winch - used quick-release connectors for that.

The reason was that the original fitting of this winch was only done with one cable - the live - to the winch and it then relied on the trailer earthing via the 5th wheel - this did not work reliably and it partially burnt out the wiring on the truck... I had to repair all that damage as well... 

Owner was very happy as it worked fine and never destroyed the indicator unit again (apparently he had purchased 5 in the past due to the winch earth...)