This may be of no value at all, but my Thomas T133 has always been a bear to start on cold winter mornings. Sometimes taking over an hour and a few battery jumps to get it going. Starting fluid is a no no with glow plugs but that didn't stop me from trying just a little spray anyway... no joy, ignites too easily causing piston to stop on the compression stroke with a clunk sound.
Then I stumbled on this simple method of getting stubborn diesels to start in the cold... a heat gun. I remove the air intake hose from the air filter to the intake and insert the snout of my heat gun into the hose leading to the intake. Turn on the heat gun (best to use low heat) and let it heat the intake for 10 minutes or so. Using the heat gun, the engine fires to life fairly easily... well, at least it does on my T133. An alternate method is to hold the glo-plug switch in the on position (manual momentary switch in my T133) for over a minute, preferably two.
If this method doesn't work, then the problem is fuel related. If it does work, then the problem is glo-plug circuit related.
Good luck.
A word of caution: Heat guns can get hot enough to melt the rubber of an air intake hose. A safer alternative is to use a hair dryer. Under no circumstances should you leave whatever pre-heating method you are using, unattended.