This always helps in trouble shooting. To check the various outputs of sensors etc in the car there is a ten pin plug tucked away (on mine it is against the firewall on the passeneger's side behind the blower motor.
Knowing the year and model it is possible to pull the spec for the electrical test adn you can check these parts through pin combos in this plug, i.e. temp wheel is holes 8 and 5 with a resistance reading of X at 65 degrees and X at 75 degress set on the wheel.

Do you have the CD for your car? Pretty cheap on ebay and it provides all the specifics for checking this stuff.

__________________
'99 S420 - Mommies
'72 280SE 4.5 - looking to breathe life into it
'84 300SD Grey - Sold
'85 300SD Silver - Sold
'78 Ski Nautique