My girls were out riding and they turned the Mule off. When they went to re-crank all they hear is a click. My ride is a 2006 Mule 3010 Diesel. The lights work, the horn works, I checked all fuses in the fuse compartment, I cleaned the corrosion from the battery terminal, and I checked that I got 12 volts from battery. When key is turned on the glow plug light indicator goes off at warm up, the transmission is in neutral and all I hear is a click. Any ideas what to check next or does someone already know the problem and fix for this.