It doesn't need to be as thick as a jump lead. I use a 2ft length of 1.5mm flex with a 15amp lucar connector to plug onto the starters T terminal at one end. The other end is simply held on the battery + terminal. It's best to get a helper to push the throttle peddle down while the cranking is being carried out to get the most air into the engine but even if you don't do that the test will still show up a low cylinder
