I just purchased a Alembic P-bass set.As I was installing it,I noticed a purple wire had come loose from the black square assembly below the 1/4 jack.It looks like there are 2 possible places it went to.Need help figuring out where it goes.Also,where does the ground from the bridge connect to also ? Thanks for your help.

No bridge ground - the system is grounded when the shielding of the cavity contacts the rivets that holds the pots together, it's automatic.  
 

Thanks Mica,John Prock said to give you a call but that solved it.

I got it installed,everything works ,but I have a bad hum when I go past halfway on the tone/treble.The bass part of the tone sounds great[DEEP and FULL] but the hum is awful.Any ideas ?

Is the pickup plugged in correctly? There is a friction lock that should engage a little retainer on the board.  
 
Also, did you shield the cavity and the underside of the pickguard? Can you post a picture of the installation? Do you have 2 or 3 controls?
 
Also, is the sounds you're hearing a low-frequency hum (like 60Hz)or is the noise higher frequency?

I'll check tomorrow and take some pictures.2 controls 1 volume and 1 tone/pan[sweep?] and the jack.

Ok ,shielded the cavity[see pics],put it all back together and nothing. Noticed another wire had come off,the red from the battery to the 1/4 jack.Checked out the schematic you provided and noticed that the 2 black wires were not soldered together.Moved them over [together] and soldered the red where it shows in your photo.Nothing. no sound no nothing.The friction lock[with 3 wires red,yellow and black] is kinda loose,but does make a connection.The hum I was hearing was kinda high[ I only noticed it when turning the tone from deep bass to treble...on the treble side]. Here's the pics

In the photo I posted at 11:18 the wires are [from the far right] purple[violet] from volume,red from battery,red and white from volume,black and another that is kinda black/purple.The black/purple is from the volume and the other is from the battery.

Make sure that the solder sides of the boards cannot contact the shielded walls of the cavity or it can short out and have no sound. If they are clear, then you might want to unmount the pickups from the shielded area (just lift them out) and see if you can get any signal that way.  
 
Are you saying that the output jack was wired completely differently on the original install? The system you have is over 20 years old, so it may be worth sending in here for testing. There is no charge to test the pickups and electronics (just pay return freight) so at least we can narrow down possibilities.

I'll try that 1st otherwise I'll be sending them in.Thanks