I beleive something is going here causing current to flow.
The ammeter would confirm that.
If all the circuits were intact with no shorts, turning the key to accessory should do nothing as long as everything is off.
But if something was on, then normally we could be pretty sure there was a poor connection between the battery and the mains splice.
However we know something is cross wired or shorting, so we'll have to come back to this.
Next break I'll look at the other test results.