In my 61 I have a temp gauge, and then an oil and generator light. When I start the truck both the oil and generator lights come on for a couple seconds. They then fade out as the the generator sppols up and the oil pressure climbs. I would imagine that is the same way that the temp light in your truck should work. I had to change the sending unit for my temp gauge to work, it didn't work at all until I did that. Good luck with the old truck!
Kyle
