gtl diesel

Hello all. I have just purchased a really beautiful running 1980 300 SD with 130k miles. It runs great but tonight while I was driving the glow plug indicator light began to flash on and off and at the same time the temp gauge went crazy going all over the place. I am thinking these events are related and maybe it's an early warning built in to the car to tell me that the glow plug relay is going bad. Am I close?? The car continues to run great and start great. No symptoms other than these.

All help will be appreciated.
Thanks,
Norm