Funny Elec issue

[Patrick110td5]

Today I turned on the 110 and my compressor which is wired under the back seat turned on. No lights or anything on the dash (glow plug and battery etc not lit) turned on and off again a number of times to no avail. The compressor would turn on each time even though my dash mounted switch was off.
Gave the battery cables a jiggle and they were secure as they should be then next time I tried to start it cranked straight away like normal.
Luckily this happened at home when I wasn’t in a rush, but would anyone have any ideas where to start diagnosis?
My thinking is it’s some sort of earth issue. Landy had been driven in the pretty heavy rain earlier that day so I wonder if something was wet.

[dero]

Does it run through a relay ?