2009 Yamaha electric cart problem

[beachbum22]

Hi, just bought a 2009 yamaha golf cart!, the problem i am having is when i move the switch to forward or reverse and the key on the cart wont move?
the batteries are fully charged.My friend came over and switched the tow/ run switch a couple of times and then the forward/ reverse started working? after that we drove the cart for a couple of miles, got home and put on charger again!the next day went to drive the cart same problem? wont move in forward/ or reverse. Iam lost any ideas its under warranty and the shop says they cant find a problem? its working fine for them? they still have the cart in the shop. Thank you for your help?