What you are measuring is resistance quantified in ohms.

All you need is metal to metal contact on both probes... the electrons will sort themselves out no matter how small the contact points are. Removal of heat shrink is only needed if you cannot make a decent metal to metal contact with your probes, or your measurements don't add up hence where the advice from Simon and Sprog makes sense. If the measurement you make makes sense to you then there is no need to remove the heat shrink. Pushing the probe through the heat shrink is a last resort, try for other places first or try to get to exposed metal at the ends of the heat shrink.

If there are two or more wires to a particular measurement point then you will likely have "resistance in parallel" Google search the term for an explanation.

8000 ohm is a reasonable value for a moderate humbucker. 12000 ohms is not unusual for a 'hot' humbucker. A Tele single coils can be as low as 5000 ohms. Seriously Hot humbuckers can be as high as 16000 ohms or more.

Two 16000 ohm (16k) humbuckers wired in parallel will measure as 8000 ohms (8k). A 8000 ohm bridge humbucker and a 7000 ohm (7k ohm) neck humbucker wired in parallel will measure close to 3750 ohms (3.75k ohm). Pots in humbucker guitars are usually 500000 ohm (500k) types and often can be hidden to meters by their high resistance value when compared to PU's.

If you measure across the output jack and the meter see's/measures 500k then the the wiring is not letting the PU be seen by the jack but the meter does electronicaly see the volume pot.... It IS simple logic like that... Measure across the output jack, volume set to max (10) and in our example above you get 7000 ohms, then yes the neck PU is the only one connected to the output socket....
And a telling one is the meter is measuring across the output socket and it shows zero ohms, which most often means that the selected PU is shorted to your shielding somewhere inside your build.