Unless your tractor usually requires glow plugs to start, I would cut every single wire that connects to power (the battery) in any way except for the main cable to the starter and then just use a jumper wire from that terminal to the start terminal on the starter and start the engine. I would only do this if it were absolutely necessary to move the tractor right away. A diesel engine does not require any power to run, some/most diesel tractors have an electric solenoid to kill the engine but most also have a manual safety kill handle that is usually cable operated. In the case of a burnt/damaged cable, you could trace the cable down to the injector pump and operate the kill linkage by hand to stop the engine. Good luck with it !!