[spokeshave]

I can’t think of a way to do it that does involve putting an ammeter in series with the battery and pulling fuses one at a time.

Don't need an Ampmeter.

just touch/scrape the wire on the battery terminal and see the spark....pull out one fuse at a time to locate the circuit.

If that doesn't work there is a short in the wiring somewhere..

Happened to me...eventually found a short in the wire leading to the rear upper cab light.

[Steely Tom]

Good idea! You can even use an AM radio to detect the sparking much more sensitively than you nan detect by eye. Of course you won’t be able to use your car radio for this purpose. Well actually maybe you could as long as the drain isn’t on the same fuse circuit that carries the radio supply current.