not sure what the jack is for at the top of the body but still a gorgeous bass
 
http://www.ebay.com/itm/ALEMBIC-TRIPLE-OMEGA-JOHN-PAUL-JONES-JPJ-BASS-led-zeppelin-/321093668942
 
~Taylor

after looking at it again it doesn't look like another input jack but I'm not sure what it is suppose to be

Taylor,
the text is saying that this is an additional strap lock which is installed into the wood.... strange idea....
Oliver (Spyderman)

Generally speaking, most basses don't have any input jacks. Just saying...
 
I suspect most would prefer the look with the strap button on the back, but I can see that one might prefer the hang angle with the strap in front.