Offroad-Express

I'm running my 2L diesel plumbing on my new (to me) 5L motor, its got what toyodiy refers to as the cold weather pack. I know that unit with the metal lid on it (on the left) is meant to be a diesel heater, can someone tell me what the unit is with the black rubber cover on it and wire out the top and what it does? Toyodiy only calls it a relay/switch no reference to what it does, there is a fuel pipe on the bottom which then runs in to the top of the fuel filter.
Cheers
Nick

I know this unrelated but you want to throw the inlet manifold away and fit a NZ new 3L one with a 5L aircleaner otherwise you will be gutless as hell.

Those manifolds only have a 60-65mm hole . The NZ 3L is 75mm.

Cheers Richard