Wire gauge size for power windows?

12 awg seems over-kill, but seems to be what my M-B cars use. Why not check the wiring schematic for the RAM you pulled it from (web search)? More important is to use the right type of wire. It flexes every time you open the door. Those wires broke in one of my M-B. You want twisted wire with many fine strands. Multimeter lead wire is designed for that. The toughest environment is robotics. You might check ebay for small quantities.