Installed new batteries... golf cart won’t ingage forward/reverse

I know this sounds obvious, but make sure you have the battery connected correctly - positive cable to positive terminal, negative cable to negative terminal.

Also, maybe you bought a bad battery.  Have you had the battery checked?  Most auto parts stores will check the battery for you for free.

Check your fuses - maybe you have a bad fuse.

Maybe something broke or came loose when you swapped the battery.

If your cart is like my lawn mower, it won’t start unless you are sitting in the seat - there is a switch that is engaged when the weight of your body pushes down on the seat. Maybe that switch is bad.