300D Glow Plugs

I cannot recall how to detect the loss of one or more glow plug--does the panel annunciator light come on down to the last plug functioning, or does the light NOT come on if ANY plug is not functioning?
My '79 300D is somewhat hard-starting in the morning, and I am wondering whether all of my plugs are working.
All help will be greatly appreciated.
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Does your 79 have pin type glow plugs or the large series style?
Look at the glow plugs and how they are wired: pin type have a single wire going to each one. Series style has a bent wire with insulators on each one.

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Finally got around to checking, and mine are the pin type, so far as I can tell--one wire per.
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The light is controlled by #1 glow plug as far as it comes on or not. If #'s 2 to 5 go dead, the light will blink after you start the engine. If #1 goes dead, the light is dead. The BEST way to test them is with a remote starter button, a long thin screwdriver, and an ammeter that reads up to at least 50 amps. Disconnect the large plug on the glow relay behind the drivers h-lamp. Connect one end of the ammeter to positive on the battery. Connect the other end of the ammeter to one end of the remote button. Connect the other end of the remote button to the screwdriver shaft. Touch the end of the screwdriver to #1 glow plug. Press the button and watch the ammeter. It should go to about 40 amps and then drop to 15-25 amps in about 5 seconds. Does not move? Glow plug is open. Starts low and climbs? Glow plug is shorted. Do this for all 5. Just using an ohmmeter is totally misleading. It will only tell you when one is open. With age, the glow plugs melt and they short out.

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Thank you very much. I will add this to my document collection for MB systems checks--better than all of the manuals I have collected over the years.
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