I bought a used 2015 mule pro fxt ranch edition. I was having a problem with the winchworking intermittently. when I checked the voltage going to the control box it was 19.9 volts. sometimes it would drop to 14v. when the voltage drops the winch would work. it's the same at the auxiliary fuse box under the hood. this is a kawasaki dual battery system. any ideas as to why the voltage imwould be so high?