Originally Posted by SouthArk370Z

Conductor material - not that important for your purposes. I'd go with Copper but Aluminum will work fine.
Strand count - the more strands, the more flexible the wire will be.
Insulation - Needs to be rugged enough so that it doesn't get cut by body/frame parts.

THHN is a general-purpose insulation that can be used just about anywhere on a car. The nylon jacket provides good cut/wear resistance. But there are many other types of insulation that will work just as well.