Tractor Repair: farmall m not charging battery, field terminal, charging battery

Question
i have a 1951 farmall m with a good motorcraft alternator on it been checked out at local parts store. and works find. we rewired the tractor but still won't charge the battery. put new amp gauge in it and nothing happens on the gauge. this tractor is set up for pulling with kill swicth on it. not sure what to do next could use some help. thank you

Answer
Hello,

  I only use Delco alternators, so I am not as familiar with Motorcraft, but some things are the same no matter what brand it is.  An alternator must have power fed into it before it will start charging.  Make sure there is power at the field terminal of the alternator when the ignition switch is on.  Try checking the charging a different way besides looking at the amp gauge.  Hook up a voltmeter to the battery or to the output terminal of the alternator.  A good battery should have about 12.5 volts when the engine is not running, and about 13.5 to 14 volts when the engine is running if the charging system is working.  Make sure the amp gauge is wired correctly.  An amp gauge must be wired in series, so all the power from the output terminal of the alternator must go through the amp gauge before it goes through the rest of the system.