I went to the Sears web site and looked at the parts diagram. Looks like not very much to the electronics on this mower. It looks like 4 12 volt batterys to get 48 volts, battery charger, switch on the handle, and motor. If you don't have one get a multi-voltage tester. I have seen cheap ones for around 5 dollars. It looks to me about all you can test is see if your batterys are puting out 48 volts. Looks like everthing is a sealed unit like the switch and motor. As I said before make sure the chassis ISN'T grounded to the battery. If I had a wireing diagram I could tell more.