8N ignition problem

[PhilWV]

8N, front distributor, 6V positive ground. You all were very helpful the last time I had ignition problems a couple of years back, so I'm hoping you have some insight into my new problem. Tractor was running reasonably OK until after it sat for a few weeks. Now no spark. Here's what I've done so far:

1. Checked voltage at the coil: 6.35V (same as battery) with points closed, 2.5V with points open.
2. Pulled the distributor and followed Bruce's very detailed directions to make sure everything was in order.
3. Put everything back on the tractor, still no spark. None at all, not even a weak one.
4. Measured spark plug wires for resistance, they all check out at 0 ohms.
5. Hot-wired the coil from the battery - STRONG spark.
6. Thought the coil might be bad, so I switched out the old one, which I got from Tractor Supply a year ago or so, for a new one from a well-known online retailer (the one named after a large river in South America). Same problem: no spark unless it's hot-wired straight from the battery.

Before I conclude that the new coil is also bad and order one from a more reputable source, is there anything I've overlooked?

 

[old]

8N, front distributor, 6V positive ground. You all were very helpful the last time I had ignition problems a couple of years back, so I'm hoping you have some insight into my new problem. Tractor was running reasonably OK until after it sat for a few weeks. Now no spark. Here's what I've done so far:

1. Checked voltage at the coil: 6.35V (same as battery) with points closed, 2.5V with points open.
2. Pulled the distributor and followed Bruce's very detailed directions to make sure everything was in order.
3. Put everything back on the tractor, still no spark. None at all, not even a weak one.
4. Measured spark plug wires for resistance, they all check out at 0 ohms.
5. Hot-wired the coil from the battery - STRONG spark.
6. Thought the coil might be bad, so I switched out the old one, which I got from Tractor Supply a year ago or so, for a new one from a well-known online retailer (the one named after a large river in South America). Same problem: no spark unless it's hot-wired straight from the battery.

Before I conclude that the new coil is also bad and order one from a more reputable source, is there anything I've overlooked?

A reading of full battery voltage with the points close tells me the point either need to be cleaned or replaced. The reading you got seem back wards You should have lower then full battery voltage when the points are closed and battery voltage with them open

 

[JMOR]

Your points open/closed numbers in 1), seem backwards.
Start measuring voltages, going back up stream toward the battery.. coil, ballast resistor output, resistor input, 3rd terminal on same, input and output sides of ignition switch, ammeter, and finally the wire from battery cable connection at solenoid which feeds ammeter.

 

[PhilWV]

I see. I must have gotten the voltages backwards for points closed vs open.

Points open gives me 6.23 everywhere.

Closed: 6.23 between battery terminals
6.20 at ballast resistor (battery side)
2.45 at ballast resistor (coil wire side)
2.45 at coil terminal

 

[PhilWV]

To bypass any poor wiring connections I ran a wire from the negative battery terminal to the top right pole of the OEM ballast resistor. Then another wire from the top left pole of the resistor to the coil. No spark. Hot wired the coil to the battery again - strong spark.

Resistor reads 4.5 ohms between those poles.

Do the resistors ever go bad?

 

[old]

To bypass any poor wiring connections I ran a wire from the negative battery terminal to the top right pole of the OEM ballast resistor. Then another wire from the top left pole of the resistor to the coil. No spark. Hot wired the coil to the battery again - strong spark.

Resistor reads 4.5 ohms between those poles.

Do the resistors ever go bad?

Yes resister do go bad but could also be a bad wire

 

[JMOR]

To bypass any poor wiring connections I ran a wire from the negative battery terminal to the top right pole of the OEM ballast resistor. Then another wire from the top left pole of the resistor to the coil. No spark. Hot wired the coil to the battery again - strong spark.

Resistor reads 4.5 ohms between those poles.

Do the resistors ever go bad?

If it is a stock./factory ballast resistor it should be less than one Ohm cold and when enough current to turn it a glowing red it is around 1.7 Ohms. Temperature dependent. I say either resistor or dirty/rusty connections to resistor windings.

https://imgur.com/XaaFeYj

 

[Mad Farmer]

Check for bat voltage to the key, then from the key (ON). If OK your key is good and have voltage to the resistor.

Then check coil side of resistor key on, should have voltage depending if points are open or closed. If no voltage jump across the two poles on the resistor, key on. Bat voltage on coil side? If yes resistor is bad. If resistor is OK then wire to the coil may be bad.

Run a jumper from coil side of resistor to coil key on. Voltage at coil/starts?

 

[PhilWV]

Check for bat voltage to the key, then from the key (ON). If OK your key is good and have voltage to the resistor.

Then check coil side of resistor key on, should have voltage depending if points are open or closed. If no voltage jump across the two poles on the resistor, key on. Bat voltage on coil side? If yes resistor is bad. If resistor is OK then wire to the coil may be bad.

Run a jumper from coil side of resistor to coil key on. Voltage at coil/starts?

Thanks. I bypassed the key first thing, got battery voltage to the key side of the resistor. Put a jumper wire from the coil side of resistor to the coil. No spark, and voltage was on the low side <2.5V. Sparks great when I bypass the resistor and go straight to the coil.

New resistor comes Friday. I’ll pop it in and report back.

 

[PhilWV]

Back with an update. It was indeed the ballast resistor. I made the mistake of ordering a cheap one from a well-known online retailer named after a South American river that was deficient in every possible way... ordered another from this site and had a much better result. Tractor runs better than it ever has since I've had it.