Hi

The answer is you shouldn’t!
There is no advantage to running the alternator B+ wire disconnected.
First of all it’s not recommended at all.

Some people use to think that if they removed the positive cable the car should run on it own power from the alternator. This proved the alternator was working.
At that very moment yes but questionable later.

It would be like running your engine up to red line from idle.
The engine is not made to ever run up that high without a load applied.
A car traveling in its top gears shouldn’t ever the reach red line.
In fact there is a lower limit for endurance reasons.

The D+ current from the dash is there only for initial startup magnetism. It has a current output limit.
Like priming a water pump.

The alternators exciter circuit uses a regulator to loop the feed from exciter diodes in reference to the system voltage it sees from the B+.

If it sees no voltage it’s is possible for it to dump all the exciter feed into rotor.
Then there is excessive current made in the stator.
That increase output goes out towards the main diodes in waves.
The diodes on either side of the alternator have saturation limits.
That’s probably where the 14 volt specifications is noted.

The alternator output needs to be absorbed by the system of headlights, and blowers. Those and the battery is like a shock absorber.
Don’t disconnect it!

You must think you need an amperage meter, with plus and minus hand to show which way the current is flowing?
That’s old school but I have a clip on induction amperage meter that stays around in a storage drawer.
It’s a hand held meter for checking starter current draws. It will also read smaller charges towards a battery too.
It’s left over from my 1974 Ford days of dash amperage meters. Oh how Useless as it seldom wiggled.
Big case with vibrating points type regulators too.

Clean the engine block ground to the battery or Take the alternator out and have it load tested at an auto electric shop.
They might give you the straight skinny versus some parts chain stores.
They just trade boxes.


Phil