I’m helping a friend with his quad it’s a electric start when we try and start it it sounds as if the starter is just spinning not cranking over at all I checked the wiring everything is correct so I got a feeling to try and hook the positive to ground and ground to the positive directly to the starter and it kicks over like regular I don’t understand I was hoping some one can shed some light on my issue.

 

Sounds like the polarity got crossed somewhere. Use your voltmeter to check polarity to the starter

 

Wrong starter brushes. Some Yams have starters with brushes that make it turn one way, some that make it turn t'other. Your "friend" has put the wrong ones in for a 125. Or bought the wrong starter motor.