There's a sensor just below the valve cover right next to the IP that connects to the wire bundle that supplies the glow plugs as well.
There's another that connects to the same wire bundle on top of the coolant outlet.
Are they both coolant temp sensors?

There's one more on top of the coolant outlet that has two vacuum line attached to it. What does it do?

Uh, 123, 126, or truck?

See answers in bold.

__________________
1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
Monark Nozzle Install Video - http://tinyurl.com/ptd2tge

Thank you!

On at least some chassis, that would be the low temp cut-out switch for the cabin heat. It prevents blower operation before the engine warms up.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

It was from 300D and i did mange to find some info from the FSM and it's marked 100C fan switch on one of the diagrams.

And were those diagrams specific to the 1983 year model?

How many wires go to your switch?

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Yes, I got it from startekinfo, and it's just one wire.

Sounds like the low temp cut-out switch to me.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.