Mystery circuit in Transit campervan

[tapkaJohnD]

My Mk6 TRansit day van has no 'comforts' at all, just a bunk bed, but does have a 'hook-up' built-in, that the DPO seems to have used for a domestic microwave! I found this accessory circuit on top of the battery.

One 10A feed goes to two switches, nicely fitted to the dash. One switch controls the interior lights in the back, and the other comes back to the relay on the wooden board. That switches a supply with a 15A fuse, and there are two more 10A fuses. The wires rom all three disappear up the B-post and into the back of the van, but I'd prefer not to dismantle the lining to trace them.

Can anyone suggest what such a van might need this relay for? Thanks!

This is the circuit, drawn out:

[OutInTheShed]

My guess is that it could be to switch in a second battery, for charging while driving.
Not sure what other loads might be wanted to be controlled from the driving seat, maybe a diesel fuelled heater?

[Murph7355]

Electric nipple clamps in an ex-torture/S&M wagon?