On my ACC panel, if I press the "rest" button for five seconds while driving, it cals up the diagnositics panel, giving the readout from many of the car's sensors.
I can check coolant temp, interior temp reading, bumper-mounted outside tep sensor, heater core temp, AC pressure, refrigerant temp, rpm, road speed, and charging voltage to name a few.
I can't remember how to call it up on your pre 1996 ACC unit, but it can be done. Check David C Klass' posts on this subject...
as well as this link:
CLK 430 Problem