That would be these things:
I think they are actually on that other picture, they are probably masked because of the angle of the shot, as they do not go straight back, but are angled upwards slightly as they go to the rear, as evident on the drawings, the larger of which ought to assist you in placing in relation to the panelling line.
UT and GHG (marked on the photograph), pinpoint the locations of the Underwasser Telegraphie, and the Gruppenhorrchgerat. These being the underwater telephone systems for intercommuniction between U-Boats (also sometimes known as Gertrude). GHG is the 'Group Listening System'. Early boats had an array of eleven sensors, later ones had 24, which is the case in that picture.
To be honest, I'm not entirely sure what the purpose of the wire was, but it seems logical to asume it is something to do with the GHG, since the wire, if it goes along the inside of the fixed forward part of the bow plane, would terminate near the GHG sensors, and it does appear to have electrical insulators on it near the hull. Of course it could also be to prevent the tip of the plane fluttering during reversing, but how effective a single wire, as opposed to a pair, would be, is hard to say. If one equates it to the bracing on a biplane wing, then I'd imagine two wires would be more effective. I do know that the part of the dive plane which the wire is fixed to was a fairly substantial structure on U-Boats, because if you look at U-534 (the Type IX in Liverpool), that is the only part which remains, the rest having either broken off or (more likely) corroded away.
The wire (whatever its purpose was) can certainly be found on drawings of all marks of Type VII subs, although it often doesn't show up on them, so I'm guessing it was a standard feature.
Chock