Jayco isolation switches (when fitted) are normally just inside door.

LED's sometimes are thwarted by voltage problems; check your battery is at full charge.

Remove LED globe and check if you have power to fitting, with meter or test lamp.

Someone who is an automotive sparky may have other suggestions

The kill switch is usually on the rooftop edge , on the outside of the canvas,it makes contact with the edge of the van when it is lowered,it is near a corner post.
It turns off the interior light to stop them burning a hole in the canvas,when the bed end is push in and the roof is lowered and the light switch is left on.
Which happened to us years ago when we had a Jayco Dove,them days the lights were incandescent and had a fair bit of heat.
Hopefully it just a sticky switch,

Thanks everybody - I have just found the ever elusive plug right near the stove - I had been wondering what it was for! Duh!