Glow plug dash light not working
 

1982 300 D turbo, 169k miles.
Okay, so I have searched and searched, there must be a million threads on glow plugs, and I have read most of them, or at least as many as I could before I was distracted by a squirrel.
My glow plug indicator light on the dashboard does not light up.
I have checked it with a multi-meter (mm) and it gets no power when the key is moved into either position. All of the other db indicator lights come on (battery, brake pad level, parking brake and seatbelt) and I checked the seatbelt light with the mm and it has 12.5 v when lit.
I checked the relay with the mm, it has 12.5 v at the main, 12.5 v at both sides of the strip fuse. The relay has 0.3 or 0.4 ohms at each socket, which means that all of the glow plugs and wires are good. The relay pins all have 12.5 v each during the first phase of ignition, then the relay clicks and all the pins go to 0.
Car cold starts immediately and runs well, no sense of problem with it starting or running at all.
I just want the glow plug indicator light to work. What else is there to check, what else can be causing this? Thanks, Alex.

The only thing it can be is the relay or glow plugs......just ohm'ing the plugs will only tell you if they are open.....they really need to be remove and tested with jumper cables to confirm the tips get hot and not the body of the plug....if they are all working, holes reamed then it would be the relay...I would assume....

From your mm readings, Id be popping the instrument cluster out and check your bulb

Check resistance at pin 3 of the smaller plug to ground. If it's open, you probably have a burnt out bulb.

So I guess I didn't explain myself properly. When I said "My glow plug indicator light on the dashboard does not light up. I have checked it with a multi-meter (mm) and it gets no power when the key is moved into either position.", what I meant was that I DID pull the dash, and check the bulb, and replace the bulb with new, and remove the bulb and put the multi- meter in the socket where the bulb goes, and got zero reading with the key in the on position. So I'm pretty sure it is not the bulb.
As far as checking the ohms on the sockets of the relay, maybe I'm a little confused. Can I have a bad glow plug that measures less than 1 ohm resistance and still tells the relay to shut off the indicator light on the dash?

a good glow plug should pull .5-1.0 ohms. .3 is too low
also, with a GOOD battery, voltage will drop to 11.5v when the GP's are energized, and gradually rise to 12.0, maybe 12.2
if you are reading 12.5 on each GP when the key is turned, you have several bad glow plugs, and you must have great compression to start the car easy.

pull them all, change them for new Bosch plugs, and see what it does.

test the ones you pull out with a battery, like the DieselGiant.com glow plug thread shows.