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Many no starting, lack of electricity to instrument panel situations can be attributed to poor earth(ground) connection. I need your to explain in more detail what you mean when you state fuel gauge &n other instruments go hard left. No starter engagement could be as simple as none operational neutral start switch(item 8 or 31). If ground cable is still attached to battery box or tractor frame I suggest to relocate ground(earth) cable connection to starter mounting bolt or engine block.