Hi,
I am new to the forum, sorry if I am bumping this post (doesn't seem all that old).
I have recently acquired a Hohner B-Bass too, a slightly different model with the battery in the same compartment as all the wiring and the pre-amp, I am not sure if it is older or newer. But anyway, I did some research when I got it, in case I ever needed to fix it (it worked absolutely fine when I got it) and found a wiring diagram in an old basschat discussion at:
[url="http://basschat.co.uk/index.php?showtopic=44498"]http://basschat.co.uk/index.php?showtopic=44498[/url]
Just passing it on in case you are still interested.
This is a cracking bass, I hope you manage to fix it!