Rob, My Merc 1500 has solid stranded stainless steel core wire i the spark plug leads. It's resistance is zero..... I believe most outboards are the same...
why do you need to know what the resistance is? Buying new wires or just testing them or what? If you dont have a spark plug tester (nice thing to have if you plan to work on the boat yourself) then take your boat out at night and start it up with the cover off and check for any arcs.
