FED, you beat me to it.
I think that that is the grounding cable on the refuelling hose. Grounding to the aeroplane, that is.
Ref the Beverley,I posted this some time ago on another forum
Early 60's I had the good fortune to be sent on a French Air Force skiing course. There were a load of French Air Force pilots on the course as well.
One recounted his version of the Beverley's first demo flight at Farnborough.
According to him, on the approach to Farnborough, the captain realised there was a crow formating on the aircraft. Captain puts on more power, crow flaps its wings a bit faster, more power, more flapping, etc. Eventually,Bev is flat out, crow is hardly raising a sweat. Captain pulls off the power, and puts down the flaps and raises the nose. Just getting a bit of burble, when the crow flicks and spins in.
Not sure the french were overly impressed.
It sounded good in French - " il y avait un grand corbeau noir" .