Outer Limits 4x4 Board

OK in the lower thermostat housing there are TWO plugs... the Gregory's manual says the small one (toward the front) is the temp sender unit, so what is the larger one at the rear for?????

I'm told the factory temp guage is notoriously innaccurate, only 3 or 4 degrees moves it from a quarter to three quarters?

So what's better, a mechanical or an electric aftermarket one? I saw the "Speco" ones in repco, it looks like the mechanical one will fit it's sender into the smaller of the two (ie the factory one) and the electric will fit in the other one (the unknown one).

I'd rather have the factory one also still working if poss, just like to see exactly what temp relates to where on factory guage.

Any thoughts appreciated.

the other one is for the glow plugs. tells the unit whether to come on and for how long.

Ah yeah should have thought of that... brain fade, thanks.