What are these wire's coming from Jazz bass pickups?

They are part of the ground circuit and usually are either at a 'star' spot where they all come together or soldered to the back of the pot as you see.

Ultimately, they are all hopefully grounded to the amplifier.

 

There are ideas that if you do it incorrectly (whatever THAT is) that you can create a ground loop and cause some untoward problems concerning interference. I've heard OF it although never actually experienced it - that some powerful radio stations can enter the signal chain and get to your amplifier.

People can also tune the KGB in on their dental work or so I hear. Maybe. I CAN get some noise when I get near my computer tower however, but that's not a standard operational procedure.

The 'Star' grounding is what I have on most of my gear, although I also see the common ground being created on the back of a pot too.

Either way, I don't hear any problems and I certainly never hear radios, humming, RFI nor KGB secret broadcasts on any of my stuff - so maybe I'm just fortunate. I dunnow.

The only time I'd worry about heat shrinking is where a ground actually could get to lay over or very near another connection when you are packing it all together during installation.

Things just don't move around inside a guitar control panel - it's not an offroad vehicle or a NASA Space Shuttle.

 

Be sure to read the instructions carefully.
Audere preamps run the grounds differently then any other pre I have seen.