I use Gardner-Bender Ox-Gard on most electrical connections. It's zinc oxide particles in a dielectric grease suspension. The zinc oxide is supposed to be pointy shaped and harder then copper oxide, so it cuts in to the copper wire base metal as the terminal is tightened. I use it judiciously on the wire on before I crimp terminals as well, then dual wall adhesive heat-shrink. Makes for a pretty impervious joint. I also have started putting it on battery posts instead of the other options. I think it does a better job preventing corrosion than the red spray stuff, and I never cared for the shellac sealer.