It really depends on what device you are connecting power to. It is not much of a concern if running the heavier 8ga. wire, into the lighter 10ga. wire, when dealing with a 12 volt system. There are...
Yes, as long as the fuse or circuit breaker is rated for the smallest wire in the circuit, which in this case appears to be the 14 guage.
Suppose the 14 guage is rated for 15 amps and the the 12...
You can connect a 10 gauge to extend a hot 14 gauge, but not vice versa. The protecting breaker dictates the minimum size of wire which in this case is 14 gauge protected by a 15A breaker. The 10...