Searching for a fantasy book title

I'm trying to find the title of an old fantasy book I read at least 20 years ago, but I have very little to help identify it.

Obviously I don't remember the author name. i think it was written in the 80s or late 70s.

It was a classic premise with a modern day man from our world, tranported to a fantasy setting. The world I remeber was on the brink of a Ice Age and the main character and hi wizard mentor found a keep to save the human race.

In the keep they found ancient machinery to produce light, warmth and food.

Also the magic in this world was glyph based, using the true meaning of word to change reality. Obviously the main character becomes a magician even if not really that skilled.

That's it.. i think there was also a tringle with the main charcater, a princess and a dead husband who was not so dead after all, but it's all really foggy.

Ah, there were at least two books in the series.

If anyone can help me identiify these books I'd really be grateful.

Thanks in advance.

Cheers