I’ve never ever considered how tractor engines work….but I assumed the glow plugs need to be “Glowed”………..which of course takes power?

only for between 10 – 30 secs depending on ambient temp,after that it is just the fuel shut off solenoid,radio and lights etc as required.
Glow plugs are just for starting and assisting engine running for a few seconds after start.

cheers baz