I know this is an old thread, but I just installed the 12v power outlet on my Yamaha RX1 today. I did not wire the positive to the constant power in fear of some forgetful act draining my battery while I'm in the middle of nowhere (paranoid much? I know). Instead, I looked for a line that would only have power once the sled is running. I avoided the line for the headlights due to the great advice here. I ended up using a line designated for "Signals", which I have no idea what that's for, perhaps my display.
I also used an inline fuse on the positive line with a 10Amp fuse. This seems to be working great. It powers my GPS only when running, which is exactly what I wanted. Be sure to get an outlet with a rubber cap to keep moisture out.
I know virtually nothing about AC vs. DC, but..., the sled produces DC power, but the "car charger" plug for my GPS coverts or regulates it to what the device needs. Pretty simple
2003 Yamaha RX1
1999 Yamaha SRX 700