Stan, If I read you right you have a light and relay that seem to work, clicking and such. But is the fuse on the firewall in good condition. It is a thin metal strip of a thing and if it goes poof you might see the conditions you describe.
Wires to the senders on the coolant flange are for temp gauge and glowplugs. Not quite sure how the Caddy is set up but all you need to do is try one on the first sender and see if the temperature gauge works in the car or not. This providing the engine is warm. If no movement try it on the other sender. Once you get a working temp gauge put the other wire on the other sender. Now the GPs should not be needed as the engine is warm. No relay clicks?
Search the threads for keywords like temperature gauge, temperature or temp sender. Seems like we have had this discussion of late.