Gray/grey roofing cement or silicone rubber would keep the water out. Then, painting the entire cable with some sort of rubberized waterproofing paint, when the weather gets better, should provide enough protection unless something hits the cable and knocks the paint off. A pice of cardboard placed behind the cable would keep whatever you coat it with from getting on the house siding itself.

I think most of us thought the insulation problem was at the "head" where the wires go into a vertical pipe and/or make a sharp bend and the insulation usually deteriorates there first.