No Thermostat in my 560 SEL?!

[TheHof]

So after having my 1989 560 SEL for 10 years I went in to do the thermostat today. I followed the tech page on here and I am pretty confused .... I don't see a thermostat. Is it actually located on the side of that housing and entering in sideways?

Also, the Coolant Sending Unit (?) plug vanished in the process - it must have already been loose. WTF! My fear is it actually fell into the what I thought was the thermostat housing. I can't find it anywhere. As usual a very simple job turned very frustrating - so essentially situation as normal in car repair.

So I guess the bottom line is, where the heck is my thermostat? And for the Sending Unit harness plug, if it DID fall down in there any ideas on the best course of action? But then again wouldn't it float ...

Thanks in advance for any help.