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Easy, Ive seen a lot of them that dont fail electrically but fail cuz of moisture or rust or corrosion making the needles stick. If the tractors not running and you turn on the lights and ignition, they ought to swing over in the - discharge direction. Does your needle ever move at all????? ?? Does light tapping on it make it move at all??? I cant really recommend this lol but if one had a light gauge like No. 20 or so wire attached to its Load (NOT side to battery/starter) terminal and scratched its bare end to frame ground, the needle sure ought to swing over in the - discharge direction as that wire sparks or else the meter is shot or stuck. Its safer if you attached a load like a light etc to the ammeters laod side to see if the needle ever moves to - discharge as it should. An ammeter is like a short circuit almost, if its wired right, the Supply side (to battery/starter) ought to read hot battery voltage and likewise UNLESS THE METER IS BAD/OPEN its other Load terminal must also read hot battery voltage (or else its open n bad) Even if its mechanically stuck (often the case) the charging system can still charge the battery unless the meter is bad/open (rarer). If the lights get brighter from idle to wide open throttle shes charging. Likewise, if the battery rises in voltage from 12.6 to 13 to 14 (half that on a 6 volt battery) as the engine is revved up, shes charging okay even if the needles stuck. I seldom see then become a bad open circuit, but Ive seen a lot of them with stuck needles from rust or water or corrosion. John T Nordhoff in Indiana, retired electrical engineer
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