I also noticed that the plugs would stay on for a long time even when the engine was warm when restarting.   I figured the most likely culprit was the relay.   While the best thing to do would probably have also been to test each of the glow plugs, the symptoms seemed very much in line with a bad relay.

I looked up the part number for my car and came up with 002 545 0532.   There were a lot of options for this.  I think OE was VDO or Stribel.  At the time of purchase, neither were available.  As I write this, Stribel seems to be at around USD$255.  There were a few brands available and I went with Huco, which seemed to be made in Germany.  It was about $55USD.

Swapping out the relay made an immediate difference.   The glow time was much shorter and the car still started very easily.   I’ve been driving it around for a few months now and I’ve not had the light come on at random times again.

Interesting, when I start the car from cold, the light goes out, but comes on very faintly when the car is running for another minute or so before going out.   Not sure what this means, but everything seems like it is working as it should be.

The old relay was clearly the original as it was dated 12/80 which is in line with the build date of the car.    I’ve kept the old relay as being original is probably rebuildable.

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