Identifying the circuit responsible for a parasitic drain, can be a real challenge. Modern vehicles have a great many circuits, supporting a great many selection of electronic modules and components, to choose from.
Initial visual inspections are always a good start. Looking for obvious signs, like displays or lights remaining on, is always nice for a quick diagnosis. Unfortunately that rarely happens, in my experience and if it does, then I’m unlikely to get the job.
Very often, if there is a parasitic drain, the drain is quite low. That usually means the vehicle battery goes flat in a couple of days or so. The drain may only be 100 or 200 milliamps.
The first thing we need to do, after confirming the fault, is identify which circuit is responsible. That way we can narrow the search. Volt drop testing the fuses, is a reliable method, even if it’s a painstaking method.
Remember; where there is current flow there is volt drop.
Please check out this short video: https://youtu.be/4q5iYkCtfWk