A while back I had a minor problem with intermittent no spark on my 150cc Hensim GY6 quad. It was caused by a flaky tether kill switch which I have since replaced. But I didn't have a wiring diagram so I got a little obsessed and traced the whole thing out from stem to stern. In case this might be of help to others with wiring issues I'm going to attempt to post it. I've never done this embedded picture thing before, so lets see if it works:
I converted these to jpegs for photobucket.com. The original jpegs are very readable, but photobucket has blurred it up a bit. I think it is still readable.
The schematic was drawn using the free schematic capture program at ExpressPCB.com. I have the source files if anyone needs them.
Not having a wiring digram can make a simple job much more difficult.
Lynn Edwards