The Big red wire goes to the starter and continues to the alternator.
From the wiring diagram it looks like the the junction might be at the starter terminal. The starter takes maybe 200+ Amps and The Alternator might charge 80+ or so amps so they are the biggest +12V wires.
Can you get a look at the setup at the starter terminal? If there's two wires
then you remove the one to the alternator and see if your unwanted current drain
disappears.

Plan B take the heavy red wire off the alternator to test.

Also look for corrosion or junk on the starter terminal lug that can act as a resistor.
If you pull the wire/s off the starter lug measure with your ohm meter
from the starter terminal to ground It should be open/ No resistance.
If you see some resistance then the starter/ solenoid has a problem causing unwanted current flow.

Is the car in the salt belt?

FYI your battery should measure 12.6VDC with out the engine running
Charging 13.65 seems a little low 14.0 is about right
14.4 is too high and you'd be losing filament bulbs too fast.

Good Luck, Bill