a quick check is to just disconnect the battery + cable while watching closely for a slight spark, which would indicate something active .... do you have a modern radio with presets? do you have a generator, or an alternator with idiot light?
"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir "When we tug a single thing on an old truck, we find it falls off" ~ me Some TF series details & TF heater pics