I would say your going to have to check every wire for a bare spot. Check all lose ends for contact with ground first. Then if that does not find the problem, then you will have to strip down the harness to find where its grounding. Remember black wire is power wire for accesories. Stator wiring is green red stripe going to neutral switch, yellow, white and pink to stator.
While the above is correct for a later 175 (and many other later twins), the color-coding on a 160 is NOT identical....
160 Stator wiring is Brown, Pink, and Yellow, with ONLY the yellow wire matching electrically (purpose and connection points) on both schematics....
The Black wire is the (key) switched power buss on both bikes, and the green/red stripe is the neutral light grounding wire on both......
Dark Green wiring is the ground buss on the later bikes, but on the 160 is the points wire, the 160 relying almost exclusively on chassis grounds.......
Please be at least reasonably sure the information you offer to help other members is correct before posting it.......
Now to the diagnostic process..... Personally, I would disconnect ONLY the ignition (key) switch, reconnecting all the other components except the rectifier.... With a fresh metric fuse installed, (and AT the main harness end of the disconnected key switch plug) jumper the red wire to the white wire..... If fuse stays intact, the taillight circuit is OK (taillight should have come on)..... Then jump red to brown...Fuse intact means Headlight and meter lighting are OK (and they should have illuminated)......Then jump red to black....Assuming previous two test proved OK, Fuse still intact means the problem is internal to the key switch itself or the rectifier.....Fuse now blows limits problem to ignition coil, neutral light bulb connection, horn, solenoid or brake light switch....... disconnect all in the list, and then Check/connect one component at a time until fuse blows....That's the culprit
