Check this link from AllTrax. This is a very informative document. It explains in detail the controller, solenoid, diodes, and resistor parts of the cart. Very good reading. This will explain alot. It has charts to help in sizing your solenoid to controller amperage as well as the diodes and pre-charge resistors. This applies to all controllers, just look at the amperage. Pre-charge resistor is size by cart voltage and diodes are sized by the amperage you controller is.
http://www.alltraxinc.com/files/Doc1...ns-Learned.pdf