This is more then you need and was taken from my Troubleshooting Procedure but may help: Usually the coil is way down my list of suspects for no spark, while the points or condensor are way up top. I also use the test lamp procedure although its NOT as accurate as using a voltmeter because bad points (even if new) can allow the light procedure to work but there can still be excess voltage drop which requires the more accurate voltage test. Iffffffff the coils low to distributor side is indeed at zero volts when points are closed and battery voltage when they are open that sure sounds like the points n condensor are doing their job, so if she still dont have fire out the coils top HV tower it could indeed be a bad coil IF ALL ELSE IS OKAY...
1) THE VERY FIRST THING YOU GOTTA HAVE is voltage to be present on the coils high supply (NOT to distributor) terminal when you turn the Ignition switch ON. If not she cant ever fire, but in the event the ignition switch or circuit/wire down to the coil or any Ballast Resistor is bad or open, you can HOT WIRE it by jumping a hot ungrounded battery voltage source to the coils high input supply (NOT to distributor) side n see if she runs then???? If she fires hot wired, you could have a bad ignition switch ((That can happen, when Ignition is on, the switches IGN terminal must turn hot)),,,,,,,or an open Ballast (if it has one) or a bad/open wire from switch to coil.
If the switch is good, if you turn the ignition switch on and place a test lamp on the coils high (NOT to distributor) terminal SHE MUST LIGHT UP. If not again, look for an open Ballast Resistor (if it has one, it should read around 1.25 to 2 ohms across its terminals) or bad/open wires from the switches IGN output down to the Ballast (if it has one) and distributor.
2a) When the Ignition switch is turned on, voltage should appear on the coils high input side. That would be 6 volts on a straight 6 volt system or 12 volts on a 12 volt non external ballasted system, or around 6 volts on a 12 volt system that used a 6 volt coil plus an external Ballast Resistor and the coil is good and the points are closed and they and ALL wiring is good.
2b) To insure the coils low voltage primary winding is not bad/open, use an ohmmeter and measure its DC resistance between its lil + and -terminals. If its an open circuit (no continuity) its bad/open and will NOT work. It should measure around 1.25 to 2 ohms or so if its a 6 volt coil and maybe 2.5 to 3.5 if its a 12 volt internally ballasted coil. NOTE CAUTION have all leads and any voltage source DISCONNECTED FROM the coil for this simple primary winding continuity test.
3) Next, place your voltmeter or test lamp over on the coils other low to distributor terminal side, turn her on and crank the engine over.
4) A test lamp there should flash ON (when points are open) and OFF (when points are closed) as the engine is cranked slowly.
5a) If the lamp never comes on there, the coils primary is bad/open,,,,,,,,,,or the points are never opening,,,,,,,,,or theres a shorted/bad condensor (remove its lead to points and see if lamp comes on, if so, bad shorted condensor or its wiring),,,,,,,,or the points wire is shorted,,,,,,,,or the distributors side pass thru stud is grounded (use ohm meter to test that),,,,,,,,,or the points may have a shorted spring.
5b) If the lamp never goes off as engines cranked, the points are not closing or are bad,,,,,,,,or the wire or circuit is missing from the distributor to the points,,,,,or the distributors not well grounded to the tractor.
She cant fire the coil unless its low side is getting a conductive ground return path via closed points and then the circuit is open when the points open.
Be sure the condensor or its wiring is NOT shorted out and see if the lite comes on (when points open) with the condensor disconnected. If removing the condensor makes her spark, replace the condensor.
John T
Troubleshooting Procedure
