Alainm, that sounds like the S-Chassis then. The solid yellow is the regulated AC, for lights and such, the Yellow/black is used for the tachometer (and many other places, that's just one example). I believe the Yellow/black is where most components get their ground from. You don't want to ground any AC to the chassis, only the DC grounds to the chassis (frame).
Also, the red wires being DC positive sounds the same as what I'm familiar with as well. I just didn't know if the ZX all came with a rectifier or nor. I've worked briefly on my Uncle's 2004 Legend GT, and it has electric start but I believe I did find that the lights on that machine were using DC, but I didn't know about non electric start machines.