You also want to be aware of the distance the wire is traveling from the battery to the load (light, etc.). Over a longer distance you need a heavier wire to carry the same amps.
It is also true that thicker wires carry 12v current more efficiently. Small gage wires may be able to carry the load of a single light, but the small gage also makes the cuircuit less efficient.
I don't think you can go wrong with 12 gage wire,
Most of the 12 Volt wiring in RVs is done using 12 or 14 ga. twinlead. It's important to be sure that you use adequately sized wire to meet the amperage requirements of whatever it is that you're installing. Here's a table of wire sizes and amperage ratings that will provide some basic guidelines. This table leans a bit towards heavier wire than is absolutely necessary, but that's actually safer in the long run. Remember, always provide fuse protection of any new wiring that you install. The fuse should be sized so as to protect the wiring from meltdown. For example, don't put a 20 amp fuse on a circuit wired with 16 ga. wire.
Total
Amperage
Draw |Up to 4'|4' to 7'|7' to 10'|10' to 13'|13' to 16'|16' to 19'|19' to 22'|22' to 28'
0 - 10 16 Gauge 14 Gauge 14 Gauge 12 Gauge 12 Gauge 12 Gauge 10 Gauge 10 Gauge
10 - 20 14 Gauge 12 Gauge 12 Gauge 10 Gauge 10 Gauge 8 Gauge 8 Gauge 8 Gauge
20 - 35 12 Gauge 10 Gauge 8 Gauge 8 Gauge 6 Gauge 6 Gauge 6 Gauge 4 Gauge
35 - 50 10 Gauge 8 Gauge 8 Gauge 6 Gauge 4 Gauge 4 Gauge 4 Gauge 4 Gauge
50 - 65 8 Gauge 8 Gauge 6 Gauge 4 Gauge 4 Gauge 4 Gauge 4 Gauge 2 Gauge
65 - 85 6 Gauge 6 Gauge 4 Gauge 4 Gauge 2 Gauge 2 Gauge 2 Gauge 0 Gauge
85 - 105 6 Gauge 6 Gauge 4 Gauge 2 Gauge 2 Gauge 2 Gauge 2 Gauge 0 Gauge
105 - 125 4 Gauge 4 Gauge 4 Gauge 2 Gauge 0 Gauge 0 Gauge 0 Gauge 0 Gauge
125 - 150 2 Gauge 2 Gauge 2 Gauge 0 Gauge 0 Gauge 0 Gauge 0 Gauge 00 Gauge
See the chart at for a better visual of this info
http://bart.ccis.com/home/mnemeth/12volt/12volta.htm
DEE[/url]
Grace happens...