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...I test them by substitution. I always keep a spare around and swap them out occasionally to make sure the spare hasn't gone bad on the shelf. Dell will no doubt weigh in on this one; he may tell you to replace the ignition switch; this seems to be a common problem. FWIW the first thing I ALWAYS check when a tractor won't start is the reading on the ammeter. This can be done right from the seat without disconneting or replacing anything and only takes a few seconds, so it is an efficient use of time and money to run the following test BEFORE starting to replace things: Throw the switch and, without cranking, check the current flow. It should be steady at 2-4 amps for almost all vehicles. I understand it should be at around 3 amps on N Fords, but these ammeters weren't THAT accurate when new, so 2-4 amps may be a good range. No discharge or only a fraction of an amp? The points are either bad or they are not closed. But Kettering systems almost always come to rest with the points closed. Crank the motor briefly watching the ammeter. The points should close at some point and show current flow. No current flow ever? Bad points or an open some where in the points circuit. Normal current flow at rest? Crank some more. As the points open, the meter should flicker every time a cylinder passes top dead center. Actually, the current flow goes to zero as the points open and then hops back up to 3 amps as they snap closed; but the meter shows all this as a flicker. Current flow normal but constant with no flicker? Points not opening or shorted. As Dell says, you have current flow but no spark with the points closed, and no current flow but spark with them open. "All else (is) confusion." - Milton
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