I *think* that I've determined that the original glow plug relay in my '83 300 CD has finally failed after so many years and miles. I'd appreciate anyone reading this to take a look at my diagnosis below to check if my testing is solid or not.
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Battery: 12.8 volts
GP relay strip fuse: 0 ohms
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Symptom: Dashboard GP bulb not illuminating in ignition pos. 2 (preglowing).
Test: Applied voltage from battery to female pin 3 of the 4-pin plug in the GP relay and the bulb illuminated.
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Just for fun: Probing each female pin of the 5-pin plug in the GP relay, checked the resistance of each GP and the wire to each and got 0.6 ohms.
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With the ignition in pos. 2, measured 12.6 volts at female pin 1 of the 4-pin plug in the GP relay.
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With the ignition in pos. 2 and the 4-pin female-male plug attached, measured *0* volts at male pins 1-5 inside the GP relay (these power each GP).

So...when voltage is being activated from the ignition (preglowing in pos. 2) and reaches the GP relay, the relay is sending out 0 volts to each glow plug.

Lastly, I can hear the relay click off after 20-30 seconds so the timing part of the relay seems to be functioning but again, the relay does not appear to be passing 12 volts to any of the glow plugs.

Anything that i'm not catching with this diagnosis?
Thanks-