1951 8N with side mount distributor

smorgan52

New User
Tractor keeps blowing 20 amp fuses that control spark from ignition system all the way to the distributor cap. Have 12V at the ignition, fuse box, resistor, starter solenoid, alternator, coil input and output. When I disconnect the wire that goes from the coil to the Distributor cap the voltage is at each of the previous locations. When I reconnect the wire form the coil to the distributor cap the 20 amp fuse blows. In other words when all wires are connected in the start/run sequence the fuse blows when the ignition is placed in start. When the wire from the coil out to the distributor cap stud is disconnected, the fuse does not blow but there is also no spark to the distributor. Any ideas? Thanks
 
Tractor keeps blowing 20 amp fuses that control spark from ignition system all the way to the distributor cap. Have 12V at the ignition, fuse box, resistor, starter solenoid, alternator, coil input and output. When I disconnect the wire that goes from the coil to the Distributor cap the voltage is at each of the previous locations. When I reconnect the wire form the coil to the distributor cap the 20 amp fuse blows. In other words when all wires are connected in the start/run sequence the fuse blows when the ignition is placed in start. When the wire from the coil out to the distributor cap stud is disconnected, the fuse does not blow but there is also no spark to the distributor. Any ideas? Thanks
Don't know who or why there is a fuse but it didn't come that way from the factory and from the factory it didn't have a fuse and shouldn't have one now
 
Beg your pardon. There is a fuse block with three 20 amp fuses inserted next to the resistor located immediately behind the dashl By the way this tractor is sn 434378. I assume that the 12volt conversion was done quite a while back. I just got the tractor last year.
 
Beg your pardon. There is a fuse block with three 20 amp fuses inserted next to the resistor located immediately behind the dashl By the way this tractor is sn 434378. I assume that the 12volt conversion was done quite a while back. I just got the tractor last year.
Just means it has been modified in last 70 years. Surprise, surprise!
 
I got two 8n's and neither has or ever has had any fuses. You don't need them to run the tractor. Early front mt dist tractors use a ballast resistor to protect the coil.
 
I got two 8n's and neither has or ever has had any fuses. You don't need them to run the tractor. Early front mt dist tractors use a ballast resistor to protect the coil.
True enough, but fuses might save a tractor fire when wire insulation fails due to any number of reasons, such as vibration, age, and maybe the greatest danger, mice/rats. His fuses may not be properly sized for the loads that they supply?
 
Beg your pardon. There is a fuse block with three 20 amp fuses inserted next to the resistor located immediately behind the dashl By the way this tractor is sn 434378. I assume that the 12volt conversion was done quite a while back. I just got the tractor last year.
There maybe fuses but NONE should be part of the ignition system. In and ignition system when the points are closed you have a dead short which will blow any fuse that is in the ignition system wires. Those fuses where/are part pf the light system if or when it has lights
 
BS! On “ when points are closed, you have a dead short”! I guess the Navy didn’t teach you that the resistance of an ignition coil of 1.6 to 3 Ohms is NOT a”dead short”!
Hello smorgan, welcome to YT! Standby while I interject. JMOR, I agree with you. However, one of the possible “scenarios” by the OP’s description of his symptoms would seem to suggest his coil has an internal short in the primary circuit. When the points close then the circuit becomes shorted to ground by the points through the coil and blows his “ILL” placed fuse. Is this really happening I would tend to lean more towards no. That is a fairly rare way for a coil to fail. Could this be happening? Yes, but I feel like he has something else going on.
smorgan, you are welcome to purchase a replacement coil to see if this solves your issue. However, I would prefer some more diagnosis takes place so we have a higher certainty of what the cause is. I get the feeling we may get some resistance from you when we start making some suggestions that some of the wiring on your tractor should be changed to make it work in a more correct manner. I understand that to a point but working enough to get by for x number of years is far from connected properly and working in a proven reliable manner. It would be helpful if you took some pictures of the wiring particularly of the area behind the dash where the fuses you mentioned are connected. You said it has a 12 volt conversion, is it utilizing a 12 volt generator? Or has an alternator been installed? If so what brand if you can tell? Give us a picture of it please. Where does the heaviest wire that goes to the stud terminal on the back of the alternator connect into the tractors wiring?
 
I am un clear as to which wire is being disconnected. If it is the wire to the distributor cap than I am assuming the larger wire out the top of the coil and into the top of the distributor cap. If I understand correctly than the next step I would try is to measure the resistance between the small wire terminal on the coil and the coil large wire terminal once the large wire and the small wires are disconnected. If that test is inconclusive the next thing I would try is to disconnect both wires between the coil and the distributor, large and small. Does the fuse blow if you reconnect the large wire with the small wire disconnected?
 
I am un clear as to which wire is being disconnected. If it is the wire to the distributor cap than I am assuming the larger wire out the top of the coil and into the top of the distributor cap. If I understand correctly than the next step I would try is to measure the resistance between the small wire terminal on the coil and the coil large wire terminal once the large wire and the small wires are disconnected. If that test is inconclusive the next thing I would try is to disconnect both wires between the coil and the distributor, large and small. Does the fuse blow if you reconnect the large wire with the small wire disconnected?
“I am un clear as to which wire is being disconnected.” I think he used “distributor cap” as a name for what is the “distributor”.. I think he just means the lead that runs into the distributor and connects to the points.
 
BS! On “ when points are closed, you have a dead short”! I guess the Navy didn’t teach you that the resistance of an ignition coil of 1.6 to 3 Ohms is NOT a”dead short”!
I agree the fuse box is an add on. Never seen a fused line feeding a coil.

Will 3 Ohms be enough resistance to keep a 20 amp fuse from blowing when grounded?
 
I agree the fuse box is an add on. Never seen a fused line feeding a coil.

Will 3 Ohms be enough resistance to keep a 20 amp fuse from blowing when grounded?
13 volts/3 Ohms = 4.3 amperes. 5 times 4.3 = 21.6 Is 5X enough margin?
 
I agree with Old. There are no fuses in a six volt or a twelve volt set up. Study the wiring diagrams. Do a Google search for "wiring diagrams by JMOR".


The wire is the fuse are the weak ignition switch. You can and its done all the time fuse the ignition system. I spec all of us own vehicles with a fused ignition system. The load is consumed in the ignition coil = work by no means is it a dead short event.







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Pull the cap and take a peek inside. Did this just suddenly happen to a fine running tractor or was there anything that a human did that resulted in this? Any parts recently replaced?
Your tractor has been modified if it has fuses, an alternator and a 12v battery.
 
To address a couple of posts. I did mistakenly use distributor cap as a reference for distributor electrical input for the points. I also measured resistance between the pos. and neg. studs on the top of the coil and got 1 ohm. For testing purposes any suggestion where to r;un a temporary wire to the coil from bypassing the fused ignition completely? This should tell me something. I am waiting for full set of manuals. Thanks
 
To address a couple of posts. I did mistakenly use distributor cap as a reference for distributor electrical input for the points. I also measured resistance between the pos. and neg. studs on the top of the coil and got 1 ohm. For testing purposes any suggestion where to r;un a temporary wire to the coil from bypassing the fused ignition completely? This should tell me something. I am waiting for full set of manuals. Thanks
Just use a wire to jump around the fuses.
 
To address a couple of posts. I did mistakenly use distributor cap as a reference for distributor electrical input for the points. I also measured resistance between the pos. and neg. studs on the top of the coil and got 1 ohm. For testing purposes any suggestion where to r;un a temporary wire to the coil from bypassing the fused ignition completely? This should tell me something. I am waiting for full set of manuals. Thanks
Did you take a measurement by shorting the test leads together and subtracting that measurement from 1 ohm to get a truer measurement. If the result is less than 1 ohm the coil resistance sounds low or maybe shorted. I don't think bypassing the fuses will help but might burn up some wire.
 

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