I'm intrigued as this sounds exactly like mine - all the symptoms you describe happened to mine around the time of the very cold weather at the start of Jan. I'm still trying to find a fix!
When you turn on the ignition can you hear the stop solenoid activating?
If it's not the car will not start - end of.
Before mine packed in fully it began to intermittently cutout while driving - Injection/
light (yellow box with squiggly line) would flash on along with the SERV light.
Then over next few days on startup I noticed the glowplug light would become intermittent as you describe.
Then one morning came to start and neither the Injection/
light or the glowplug light came up on pre-start check - all pointing toward an electrical issue. No power appeared to be getting through to any of the injection or glowplug circuits.
To get mine going I have had to run a fused & switched direct feed from the battery + terminal to the stop solenoid - if I turn on the switch then the ignition I get all lights as usual and it starts up as normal - however the
is registering a fault as light is staying on along with the SERV light and it appears to be in limp home mode but will drive.
One strange thing - it looked like my glowplug circuit was blowing the after ignition + fuse in the drivers side fusebox under the dash. I have now left all the glowplugs disconnected and with my wiring setup as above the car starts first time - better than with the glowplugs!!
Hope the above is of use.