Here's what I have. 85 k10 silverado 6.2L diesel
Yesterday morning, ran fine like the last several months. Did the usual manual glow switch (relay cycles fine), held pedal down to keep running until white smoke gone a half block away.
Afternoon, cranks fine but no start.

Glow relay clicks and lights when key is on.
injection pump solenoid's pink wire activates solenoid when dis/re-connected (I hear sloshing).
Square fuel filter air bleed squirts fuel fine when cranked.
pulled glow plug out, cranked and the fuel mist blasted out fine.
little or not voltage between plug and wire when cycling.

still going to
check voltage between postivie battery terminal and glow plug prong.
resistance (with key off) between glow plug prong and ground (0.8 to 1 ohm max of 3ohms).

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With a multimeter, I found:
Infinity resistance on front right two plugs between the prong and ground (engine and battery negative pole).
No voltage between the 2nd to front right glow plug and the battery's positive terminal.
12 volts between the front right glow plug and the battery's positive terminal.

In the past few years at least, in the cold, I've had to hold the manual glowing switch (that I installed) and hold the pedal slightly down to keep the engine running until warmed up and white smoke went away after driving a half block with the glow on. Maybe I left them on too long (longer than usual), burned them out and need new plugs?

I also noticed what looked like liquid under the lift pump. Maybe the pump sprung a leak and isn't putting enough pressure to the IP?

I haven't tested the relay or fusible links with a multimeter or 12v continuity light.
I also haven't tested resistance (to check continuity) between glow plug wire connectors and end at the relay connector.

I guess if the wires are ok, it's time to change the plugs and check to see if the lift pump really has a leak.

This may have to wait a few days until it stops snowing and freezing in the driveway.

 

I replaced the glow plugs with Bosch and it started. The ones that burnt out were AC Delco.