[RodB]

Your original 16mfd cap has a positive post and the negative is internally physically connected to the can. When the can is mounted to the chassis then the negative side is grounded to the chassis. If the can is insulated from the chassis then the can must be wired into the circuit, usually not to chassis ground. When you replace it with a modern cap you must follow the schematic by connecting the negative lead to the appropriate point in the circuit. So, if the cap is stuffed inside the can you can drill two holes through the bottom of the can and make the appropriate connections. There are several descriptions here on stuffing electrolytic capacitors.