Ok, still haven't changed the relay yet. I figured that the problem might reappear and I could swap them and see if it changed. It hasn't reappeared...yet...
However, the glowplug light is coming on after starting the vehicle, usually after driving for a minute, sometimes longer or shorter. I tried wiggling the key / ignition placement, but it is hit or miss if the light goes off (could be just the internal timing) and I can't hear the relay clicking if the glow plugs are still on after the predetermined timeout period.
Does this sound like an issue with just the relay, or could something else contribute?
Would the temp sensor in the head cause a problem like this? What tells the circuitry that the car is running and not to keep the glow plugs on? There isn't an afterglow system on this car.