Smokey- Copper wire doesn't know whether it's plugged into 12vdc or 120vac. What's important is the ampacity of the wire, and it's ability to handle the load. Check an ampacity chart to calculate the load and required wire size.
The loom you have appears to be a trailer light wire- typically 18 ga. May be a bit small. A 3 wire extension cord in 14-16 gauge will work.