Did you see the pic and legend on this page:

http://www.peachparts.com/shopforum/tech-help/185500-89-300ce-please-help-identify-engine-component.html

The coolant sensor has 2-prongs.

Also, take a look at Item #18 in JimF's page.

http://pages.prodigy.net/jforgione/MB_S500.html

Good luck.

Tex, 8 is the belt tensioner bolt, 12 is the power steering pump, 15 is the a/c pressure switch, 16 is the a/c reciever/dryer, 17 is a ballast resistor, 18 is the high pressure a/c line, 20 is the low pressure a/c line, and 21 looks like the cover for your coil

It's #2!

http://www.vsgardens.com/Pix/300CE/IMG_8387%20copy.jpg
Thank Nels,

the list is now complete. Thank to all of you who provided the info.

1. Valve cover
2. Thermo vacuum valve
3. Oil dip stick
4. Air cleaner
5. Fuel injector (first, 1 of 7)
6. That's the line from the coil to the distributor (some people call it a rotor). The distributor sits in front of the engine, under the plastic cover that is oh so close to the radiator fan!
7. the thermostat housing (Benz-LGB).
8. Belt tensioner bolt
9. brake vacuum hose (to assist with the power brakes, no vacuum no power brakes - BENZ-LGB).
10. Timing cover
11. Coolant hose
11a. also coolant hose?
12. power steering pump
13. ABS module
14. ABS lines
15. a/c pressure switch
16. a/c reciever/dryer
17. ballast resistor
18. high pressure a/c line
19. Ignition module
20. low pressure a/c line
21. looks like the cover for your coil

Info by Nels

Tex, 8 is the belt tensioner bolt, 12 is the power steering pump, 15 is the a/c pressure switch, 16 is the a/c reciever/dryer, 17 is a ballast resistor, 18 is the high pressure a/c line, 20 is the low pressure a/c line, and 21 looks like the cover for your coil

OK NOW I get it, when I said " temp sensor" I think somone thought I meant for the " temp guage" which is different than the " Aux fan switch" I will google for this part.