It is very common for the block heater cord to fail, and that can be replaced for about $20 or so with an aftermarket cord. Remove the cord from the heater, and test the heater for resistance. Test the cord separately for continuity on all three conductors.

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Clip your red MM lead to the nut on one of the glow plugs, w/ blk lead on BAT- (or engine block). You should measure ~12 VDC during the 20 sec the glow plug relay is ON. That is a fixed ON time, regardless of temperature. The dash bulb turns off based on temperature, but that is just a prediction: "glowed long enough to start", which is most applicable to a new engine.

If you haven't changed the hand primer from the original white plastic one to the smaller black one, do so. A new pump is ~$10 and the white ones are notorious for letting air into the fuel system.

Best way to insure the plugs are glowing correctly is to peer down the hole where the injectors were removed. You should see them glow at the tip. But, the pre-chambers vary. Early ones have a narrow neck, which can also trap carbon below, and perhaps obscure the view. Anyway, removing the injectors for a compression check and pop/spray test will likely be the next step. Member Greaser here checks and rebuilds injectors, or a local diesel shop can.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

It would start when warm even if the fuel system bleeds down over night. The 1st start bleeds the system and subsequent sittings during the day are not long enough for it to bleed down.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

I took off the injector hard lines to get to the glowplugs easier, all glowplugs were good when i tested them on an old battery, but i noticed that one injector was dry. Here is a picture of the 4th injector with fuel compared to the 5th injector no fuel. https://imgur.com/a/6Zy47 I assume this is my problem?

Do you mean fuel isn't getting to the 5th injector, thus it being dry? Delivery valve issue I suppose, maybe the DV is leaking....but it'd have to be leaking BAD for it to kill the injector.

Or do you mean there is fuel literally on the 4th injector? I don't know what to make of your picture to be honest.

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1998 Ford Escort ZX2 5 speed - 279,000 miles My Daily

1992 Mercedes 300D 2.5 202,000 - Pure junk
2000 Mercedes E320 Black - 136,000 miles - Needs repair

Don't forget to grease the screw and threads on the spring compressor.

Perhaps disconnect the hard line at the injector, crank engine to confirm lack of fuel.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

I'm surprised this wasn't mentioned, but when was your valve adjustment last done?

I always had tough starts when my valves got out of adjustment, especially when cold.

That...and a properly timed injection pump will go a long ways toward reducing cranking time.

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When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.