Sounds like the electrical connection for the temp gauge is loose and that you managed to catch the vac line to the shutoff switch and pull it loose.

Pull the cluster again and make sure the electical plug is installed completely, and take a look at the key switch. Dollar to a donut you snagged one of the vac lines while unscrewing the speedo cable, and the fix will be just plugging it back in or splicing it with some vac line if it broke.

If you actually removed the temp gauge, check that the screws are completely tight. Best to turn them backwards till you feel the thread drop into the old groove in the hole, they turn in easier that way.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!