Solved!
Thanks to the advice given, I traced the problem back to the spade connectors.
When trying the probes, one to the connectors seem to "wobble " a bit more than I expected so I gave it a gentle wiggle and it come off with few millimetres of wire. Did the same with the other and the same result. I managed to remove a small piece of sleeving to reveal the wires and the bulb test worked!
I just need to cut back a bit more to try and extend the wires to the correct length.
The only strange thing is that both of the spade connections show signs of melting.....
Thanks for your patience and all the help given.