As above, in some of the premium videos Paul is using a 4 way banana plug extension to provide a reference directly to battery neg. Im not sure of i heard him say that someone had made it for him as a gift or if they are available to purchase?
EDIT I was currently watching the latest youtube video on the Fiat 500 EPB whilst I sent this message,30 secs later Paul uses the tool and shows where to buy it!
It came from autodiagnose.eu - shop available on facebook!
