The solenoid on the back of my sons quad just clicks and the starter will not engage. I have charged the battery and still the same problem.
What could it be?
Thanks

 

You can jumper across the two main power terminals on the solenoid from the battery to the starter and if it turns over then it's most likely the solenoid! If it still does the same it's looking like a bad starter!

 

I've ran into that problem myself from time to time, check to make sure you have a good ground,, the painted surfaces on the frame and engine case are not adequate enough to give you a good ground.

I used a bit of sandpaper to make sure the mating surfaces have metal to metal contact. not epoxy paint to powder coating.