You may have a non-functioning OBC (onboard computer). Since the 1995, 48 volt Club Car's come with an OBC that regulates the batteries' charge.  When you plug the charger into your Club Car, the OBC will tell the battery charger when to start and stop charging based on the voltage levels in your batteries. As a result, golf cart battery chargers for 48 volt Club Cars need a working OBC to get them to start charging. So, it is possible that your OBC is malfunctioning and it is not the golf cart charger.  Again, this is only for 48 volt Club Car golf carts (Not for Yamaha or EZGO golf carts). If you have not manually charged your batteries and checked your connections, please do those first before assuming you have an OBC issue.

With that said, if the OBC on the Club Car is functional and the batteries are above 35 volts, you should hear a "click" from the relay inside the charger when the round plug is inserted into the cart. If no click is heard the problem is either that the battery voltage is too low (less than 35 DC volts) or there is a problem with the OBC or a fuse. The only other reason the relay will not click is if it is a bad relay (a failed "open coil"). This is very rare and there have not been many documented out-of-the-box relay failures.