Jeff in Georgia

Think most of these switches used these days are metric, use M6 X 0.75 threaded nuts: There are a lot of switch covers listed for these on eBay, here is one example: https://www.ebay.com/sch/i.html?_from=R40&_nkw=6mm+rubber+switch+boots&_sacat=0&rt=nc&LH_PrefLoc=1

Rather than cutting and splicing on a new connector end of the cable to a cable, it may be better to add on a new connecter. These have screw terminals for the wires. You may want to tin the wires or use ferrules so the wires hold well in the screw terminal. Fill the shell with grease or epoxy to ensure waterproof operation. Think I have some in the shop. Could sell you one for $15 shipped.