The light output will be the same whether you use 2 rings or 1, I tried it both ways.

CAUTION: You can NOT change the length of the wires between the inverter and the rings. I learned that the hard way. If you lengthen the wires, the rings will be dimmer depending how much you lengthened them. The manufacturer claims it won't hurt them if you do this if they are too bright for your particular application. However making the wires shorter to brighten the rings may cause premature failure. The length of the supply wires to the inverter does not matter.

14 gauge wire seems to be just fine on my car.

James