87 190 TD has a new problem. Now the glow plug light doesn't come on when the key is activated (new key and relay , worked fine for the past 4 months). It comes on after the engine starts and then goes out after a few minutes. Didn't drive long enough to see if it cycled on and off . Started easy this am at 40 degrees. Where do I start? I didn't see this problem on the other threads.

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hlg