Adding to Chris' explanation; when removing the temp gauges I first remove the throttle lever between the gas pedal and linkage at the firewall to make room for the probe to pull through the hole without stressing the very vulnerable tubes.
This requires a 7/16" socket for the two bolts holding the rod in place, one on each side of the heater box, and a 5/8" open end for the probes.
Bob
66S

I figured some one else would chime in... The gauge are held in the dash by threaded studs (off the back of the guage) with a sort of sleeve/ear that catches the back of the dash. The sleeve/ear is held on the stud by a round knurled finger nut (no flats, just round knurling). Depending on how long the car has sat in how damp of a location, these may or may not come loose. First and formost, I would spray them all with penetrating oil and let the sit. You will find that it's great fun to work under the dash of an 1800.

The temp gauge has two leads for the water and oil temp. The fluids will need to be drained from the block before you pull those two and fish them back through the firewall and pull the in-dash unit.

Hope this helps...


Chris