The answer is, it depends. It's really where ever you are able to find space for a shoebox sized charger on your golf cart. Some find that they can fit the on-board charger under the seat. This will really depend on the cart's specific battery configuration (x4 12V's, x6 6V's, x6 8V's or x8 6V's). Others will put the onboard charger on the little cubby area below the rear seat (if they have one). The Lester Summit onboard chargers that we sell have the following dimensions: L 10.95" x W 7.3" x H 4.75" and are pre-drilled mounting holes on the sides. 

You just hook up the red wire (the positive) to the positive terminal on the first battery in the set, and then hook the black wire (the negative) to the negative terminal on the last battery in the set. So, positive to positive, negative to negative. Forget about the blue wire. The ring terminals on the leads are universal and will fit on all batteries. Because all of the golf cart batteries are connected with battery cables, all batteries will be charged in series.