Weird and weirder...

There are normally 3 capacitors in our old cars, maybe 4, but..........

The one on the coil + is out of the circuit with key shut off

So is the one on the instrument cluster

And likewise one that may / not be inside the radio on the power wire

So this just leaves the cap in the alternator Those are not very big.

If you REALLY want to chase this down, start unhooking stuff

Do you have an aftermarket radio? Is it wired "hot?"

I'm speaking here only of caps on the 12V line, the one in the distributor for points is on the ground/ neg side of the coil, and is not a factor