It is important to categorize the symptoms here as we have gone to chasing electrical
ghosts that may not exist.
Cold after weeks - Good cranking / easy start
Hot start - good cranking / no start
Cool start after a day or a few hours - Good cranking / reluctant start
If these symptoms are correct I doubt you have a starter or wiring
To me this is a sign of too much fuel. I bet donuts on leaking injectors.
After the fuel is allowed to dissipate after a few weeks or a few hours the engine starts.
During a warm start, I bet you get black smoke when and if you get it started.
Another technique you could try short term is to start cranking with the fuel cutoff lever closed. After 5 seconds stick the lever in. The 5 seconds of cranking may help purge the cylinder of extra fuel.
People transitioning from car experience have been taught to floor the throttle to clear flooding. This is because on most gasoline engines you control a venturi and a wide open venturi allows maximum air in.
On a diesel you are controlling the fuel input with the throttle. More throttle equals more fuel. How to crank the engine with no fuel input? Close the fuel valve.
Your reported no rotation on start could be a byproduct of what has been happening with this engine. i.e. You are cranking a lot to get the engine started and you could be frying your starter. I don't know the duty cycle of your starter but I would get a second hand watch and limit myself to 30-40 seconds of cranking with a 2-3 minute cool down minimum between attempts.