Instrument end: Tip Ring and Sleeve plug  
Preamp end: 2 Tip and Sleeve plugs  
 
The tip of one of the preamp jacks goes to the tip of the instrument end.  
 
The tip of the other preamp jack goes to the ring of the instrument end.  
 
The three sleeves are all ground.  
 
Normally the tip is the bass pickup (neck) and the ring is the treble pickup (bridge).