Posted by 38lasalle on April 30, 2016 at 10:21:13 from (72.169.81.220):
In Reply to: Current to coil posted by GregoryKS on April 27, 2016 at 18:52:02:
Buy a cheap multimeter and take a DC voltage measurement of the BAT side of the coil (at the coil terminal itself); red lead to the coil terminal, black to the tractor frame. Should be from 6-12 volts depending on if you have a dropping "ballast" resistor or not ahead of the 12V supply line feeding the coil.
If you have voltage at the BAT terminal (with the ignition switch turned on, of course) move the red test lead to the other low voltage terminal on the coil (marked GND). Then crank the engine. If the points are working the meter will jump around as the points make and break contact. This is easier to see with an analog meter than a digital one; and a test light bulb is even easier to interpret. If the voltage stays steady and around the same as what you read on the BAT terminal, your points are stuck open or the wire linking the GND side of the coil to the points is broken. If the voltage is zero, the points are stuck closed or the lead wire running to them is shorted to metal.
No voltage at the BAT terminal means that you have a broken wire between the ignition switch and the BAT terminal of the coil, or the ignition switch is bad. Use the voltmeter to track back as far as it takes to find the missing voltage; whatever is between the "good" point and the "bad" point has to be the problem.
If you don't want to invest in a voltmeter (they are cheap and well worth the time they save, IMO) you can try the "farmer expedient" for spark checking: unplug the high tension wire running from the coil tower to the distributor center socket at the distributor (i.e., leave one end plugged into the coil) and tape the bare contact so that it is about 1/16 inch from a ground point (any piece of metal that is bolted to the frame, painted or not). Then remove the distributor cap, rotor, and the plastic points shield (if equipped). This exposes the points. Turn on the ignition switch and crank the engine until the points fully close. Then use a small screwdriver to manually flick open the points. If you are getting power to the coil and the wiring to the points is OK (and the points aren't burnt) then you will see a spark at the points and at the place where the coil wire is almost touching the tractor metal part. The high tension spark should be fat, blue, and audible. No sparks= no current through the coil.
Using cheap condensers (those from China in unmarked white boxes) is asking for trouble. These open up internally and allow the point faces to burn due to arcing. Burnt points cannot conduct electricity and the engine will suddenly stop running (and not start) just as if you had switched off the ignition. I don't think highly of Chinese points either (the point contacts aren't ventilated in any that I've seen) but the condenser seems to be the main problem.
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