When you get your probe have a play with it to see how it works. Connect the leads to a battery and use the probe and the earth fly lead to power up a bulb or an old 12v horn etc. Good luck finding your fault. I bought one of these type of probe from Snap-On tools about 20 years ago, they were about £60 then. Great bit of kit.I will check it in the morning, I've just ordered one of the probes.. I'll let you know how it goes.. Thanks for your help, its really appreciated.
Tony.