Newbie to Sprinter! which battery to disconnect b4 install steering wheel and stereo

just got my first Sprinter. it is s used one and need to swap out the steering wheel and do some stereo work.

My questions is... i think my van has the extra battery and auxiliary battery. I am confused how many batteries are there and which one i need to disconnect before i work on the car ( like the airbag and stereo...).

i see there is a Battery isolating switch, but i disconnected that ( the one next to gas pedal), car still have power...

maybe those are silly questions.... only work on cars with one battery....

thanks in advance

More information about your Sprinter will help. What model year is it? Is it a cargo van? Passenger van? Cab and chassis? An RV built on one of those? What country are you in? What engine is in the Sprinter?

2014 sprinter passenger Van at USA. it has the 2.1L liter 4cyc.

i unplug the battery isolation switch next to the gas pedal, the interior light still on? just checked, no additional battery under hood.

The main battery (for starting the engine) is under the driver's side floorboard.
If you completely disconnected the power at the shut off/disconnecty near the accelerator pedal there must
be another battery somewhere in the van.
Under the hood, under the passenger seat (in the seat box) or somewhere else in the Sprinter.
Roger