Isolator swich for auxilliaries on a crew van

[J316]

On my 2007 2,4 Duratorq 350L ( an ex Network Rail Clarks conversion ) I cannot locate an Isolator switch .
Any suggestions please.
Thanks

[dumper]

I had a look at one to maybe covert into a camper it had a switch on the dash to switch it off and on it was just to the right of the heater controls this will probably operate a heavy duty master switch close to the battery's for the clarks conversion