Copper Dont Care! you'll be good either way. The chart Artcarney posted shows even 10g wire would be ok. One thing to consider, the older TM's used more power for less lbs. But looks like your model is wired with 10g anyway which is cheaper and easier to work with.
Artcarney was right too, if your comfortable replacing the wire its better than splicing. Either way make sure your crimps are good and it you splice do everything you can to keep it dry (with in reason).
Dont forget the fuse!