Is this a single black wire, about a foot long, with a bit of shrinkwrap on one end, the other end connected to a white connector? If so, its the remote antenna, and should not be connected to anything at its shrinkwrapped end. Strange though it may seem, it does simply "float about" in the fusebox area.
The central locking problem you describe is more likely to be caused by a faulty door cath (solenoid). Hope that helps.
this morning i have checked all fuses and popped a bit of lub on the door locks
1. the door locks at the front lock with the key no problem and resistance
2. all the doors including bonnet and boot seem to shut properly
3. the internal lock button does nto seem to be working, when it is pressed whilst driving nothing happens. when i look at that buton from the oiutside when i hit the remote lock on the keyfob it flashes abotu 15 times evry second maybe quicker, then once i here the extra beep (to let me know there is a problem i imagine) the internal button flashes very quick around 15 times also/9hard to count)
i have now disconected the battery and i will leave it for a while to see if this corrects it.
while its doing that i will re search to see if anyone has had the same problem.
question, can u lock the back doors any other way as i can lock the front doors but my back doors are insecure( hmmm, wish i could think of better words there)