you need, as mentioned, a 12v rectifier regulator. standard wires from the engine should be something with RED(white with red stripe, black with red stripe, etc), thats the charge for the CDI unit. something with BLUE, thats the trigger for the CDI unit. it runs, so thats fine...i assume?
GREEN is EARTH, and is attached to both frame and battery NEG terminal. should be a strap from the battery to the frame, thats even better than some poxy wire..
then yellow and or white, these are AC from the stator. they go to the regulator. the regulator has four pins, two input the AC, two output the DC, with RED to the POS terminal (via a SWITCH or the battery discharges, usually a key switch that also kills the ignition in the off position) and BLACK to earth/battery NEG.
cant think of any bike that gets away with only four wires? other than the odd ones that have a CDI unit thats powered by the battery and thats pretty unusual... sachs madass maybe but it has a 3phase stator so has 3 yellow wires, a trigger, and earth...still five.
while most regulator rectifiers have a standard wiring pattern, some are in reverse! always an idea to test with a multimeter (with the engine running) before hooking the DC output up to a battery.
if the battery is only required for starting, (the CDI is self contained and doesnt need the battery) you can ignore the charging circuit completely. you just have to charge it yourself occasionally. should get at least ten starts if the engines in good condition before it gets too flat.
but, the starter wiring is standardly... negative of battery to frame or earth. positive to one side of relay. that can be fused, but use a big one...30A. normally they dont worry about fusing the main starter leads. other side of relay to starter motor. then the two small wires from the relay, one goes to earth. one goes, via the starter switch, to positive. stick a small(5A) fuse in that wire before the switch.
any other wires from the engine are pale green for the neutral indicator, and occasionally purple etc for gear indicators.