If the #1 plug, front of engine is dead you will get no glow light. The other 4 will still glow fine and you will be able to start the car, but it may be a little rough. Even with 2 dead I could start my car, when three went it was almost impossible on a cold (less than 40f) morning. Finding water in the relay circut board is the only difference here. I would try changing the #1 plug, if no change then look for something else. When the glow system on my 67 acted up it was very easy to figure out which plug was bad because it was a series system. The newer systems allow starting with bad plugs where the older system didn't.