Pertronix ignition issues and questions

[dbsoundman]

Hi all, I recently picked up what I believe to be a 49 8N (front mount distributor) that has a Pertronix conversion kit in the distributor, and the tractor was also converted to 12 volt, albeit a little sloppily. When I first tried to get it running, I couldn't get the starter to move unless I hooked it straight to the battery, so I knew the battery ground connection was no good. Today, I cleaned up that connection and the starter sounds good, and I'm getting 12 volts at the coil, but no spark whatsoever.

Now, I traced through the wiring, and I did see that someone bypassed the ballast resistor entirely, so the coil is fed directly from one side of the ammeter up front. I did see the extra wire coming out of the distributor from the Pertronix control unit which goes up to the top of the coil, so it also gets fed 12 volts. I took off the distributor and looked everything over and gave it a cleaning, and it looks perfectly fine. I used both a spark plug test light and tried laying a plug out by the block, and in both cases I got absolutely zero spark.

Given that I've never worked with the Pertronix, I have a few questions:

First, I read on the Pertronix site that the ground resistance from the aluminum mounting plate of the control unit to the battery negative terminal should be 0.2 ohms or less. I measured mine after cleaning things up and I was seeing between 0.3 and 0.4 ohms. Is that really too much ground resistance?

Second, I'm not clear if I should or should not have a ballast resistor connected. I got the impression from some parts sellers that a ballast resistor was required for any 12 volt coil, but I'm not sure that's true.

Finally, along with this tractor I got several boxes of parts including a complete distributor and coil, but the coil has a broken screw on the top for the wiring. I compared the resistance of the Pertronix coil (or at least the one that came with the setup- the label is not legible and it has no markings) with the other coil I have which is marked "Ford", and both measured something like 8k ohms. Is that indicative of a good coil?

Overall I'm wondering if the bad ground situation fried the Pertronix unit. I'd like to try slapping the old distributor back on it once I add the resistor back in but I really wanted to know if the mystery gray coil that is currently on the tractor will work with a traditional distributor, or if it's a specific Pertronix coil.

 

[DanielW]

While this isn't true 100% of the time, the general rule is that a 12V system needs a total of approx 3 ohms resistance on the primary side, while a 6V system needs approx 1.5 ohms (both numbers subject to a little variation). A 6V coil typically has approx 1.5 ohms across the primary side, while a true 12V coil has approx 3 ohms. Thus, in 12V systems that use 6V coils (which was the case for a lot of tractors/equipment built from the 40's to 60's), you need a ballast resistor in addition to the internal resistance of the 6V coil to get a total of 3 ohms(ish) across the primary side.

While that's (kind of) the rule for most cases, the front-mount N's with their square-can coils were one of the exceptions: From the factory with 6V, they used a ceramic ballast resistor: That resistor that had minimal resistance when cold, but would increase in resistance (up to about 1.5-2 ohms) as it ran and got hot. The stock 6V coils had about 1 ohm of resistance across the primary. This meant that there was a total about 1 ohm of resistance when cold, which would increase to about 2.5 ohms when hot. Which would normally be a little more than you'd have with a 6V system, but was what those front-mount N square-can coils were designed for.

When going to Pertronix kit, you're (kind of) converting it to a more conventional 12V system. Which means you want (approximately) a total and constant 3-ish ohms across the primary. This is usually accomplished with a new 12V coil with 3-ish ohms internal resistance and bypassing the factory ballast resistor. But some folks with their 12V conversions accomplish the same thing with the stock 6V coil and a more conventional 1.5 ohm ballast resistor in series with it. It should be noted that almost all ballast resistors are the ceramic type that increase in resistance when hot. But they usually had more resistance when cold, and didn't increase so much when hot compared to the stock resistors for the N's. The increasing resistance with temperature functions in the same way that some vehicles do that have a separate connection from the 'start' side of the ignition switch directly to the coil. In their case, they have a separate wire that gives a full 12V to the coil when starting for an uber-strong spark that jumps the gap and ignites better in cold conditions, but then drops back off once started and the key goes back to the 'on' position. The varying ceramic resistors (theoretically) do the same thing: Uber strong spark from lower resistance when starting, back to a higher resistance (and thus lower coil voltage) once everything's warmed up and happy (making sure you don't burn up the coil by putting too much voltage through for too long).

It should be noted that all those numbers are subject to some variation. 12V systems/coils often have anywhere from 2-4.5 ohms total resistance, some of the stock 6V square coils for the front-mount N's had closer to 1.5 ohms internal resistance, some of stock N ceramic ballast resistors had anywhere from 0.1 to 0.5 ohms resistance when cold and anywhere from 1 to 2 ohms when hot, etc.

It sounds very much like whoever did your conversion did what most folks would do: Replace the stock 6V coil with a 12V coil that has a built-in resistance around 2.5-3.5 ohms, and bypass the original ballast resistor. It thus sounds like it's done correctly. But a check of the resistance across the primary of the coil can confirm that.

I can't comment on the bad ground unfortunately. I'd be surprised if a difference of 0.1 ohms would cause grief, but it wouldn't hurt to clean up the ground connection.

I'm going to sound like a tedious old grumpster here. But if it were mine, I'd scrap the Pertronix kit and go back to points/condenser. Whether you stick with 12V is up to you (I'd probably stay with 12V, as it sounds like you're already set up for it). I never understood the appeal of the Pertronix kits on old equipment. It seems like once a week someone is on here asking about how to diagnose a bad electronic ignition kit. If you have no/bad spark with a Pertronix kit, there are so many hard-to-diagnose variables in there: Coil type? Ballast Resistor? If ballast resistor, what type? Bad module? Suppressor wires? Prox gap? etc. If a points/condenser system goes bad (very rarely), they're dead-nuts simple to diagnose and any replacement part costs $20 or less. And for an electronic kit to work right, all those aforementioned factors have to be perfect/correct. For a points/condenser system, you certainly want to have those factors right, but they'll usually still run in some capacity if they're off. For instance: A points/condenser system will work best with non-suppressor wires, but will still work pretty well with suppression wires. And a points/condenser system will usually run fine with the wrong resistance across the coil - you just won't be doing the coil/condenser any favours. It makes it a lot easier to diagnose and repair.

For high-speed, built-up race engines red-lining at 5000+ RPM where perfect tuning and crisp accel with perfect dwell are critical, an electronic kit definitely makes sense. For any of the old tractors we talk about on this site, you'll never notice a difference in performance between an electronic kit and a properly-installed points/condenser system. Of the dozen or so (actually, 15 I can count) old gasser tractors/vehicles I have, 14 have points/condensers. I've had one only failure of a points/condenser system: A condenser failed in a Fiat 850. Put in a new $10 condenser I had in the glovebox, and it's been running fine ever since. The rest of them have been running decades with no issue. I've had two vehicle with electronic kits, one of which failed (the same Fiat - after it failed I converted it back to points/condenser). So in my experience a points/condensers system is far more reliable. I'm sure others will disagree, however, and possibly rightfully so. Maybe I've just been lucky.

 

[Non-farmer]

Pertronix strongly recommends bypassing any and all ignition resistors on an N, including the OEM ballast resistor on the back (front face) of the dash.

I never understood the appeal of the Pertronix kits on old equipment. It seems like once a week someone is on here asking about how to diagnose a bad electronic ignition kit.

I have one and have had no issues with it whatsoever. The appeal to this arthritic maintenance guy is never having to remove the front distributor again to mess with the points. If you don't own a front mount N, you might not understand why that's a big deal.

 

[Non-farmer]

First, I read on the Pertronix site that the ground resistance from the aluminum mounting plate of the control unit to the battery negative terminal should be 0.2 ohms or less. I measured mine after cleaning things up and I was seeing between 0.3 and 0.4 ohms. Is that really too much ground resistance?

Forgot to reply to this. Have you checked the resistance of your meter leads? It's possible the extra you're seeing is just that. Touch the leads together and if you see any resistance, you need to subtract that amount from any other reading you take.

Otherwise, I strongly recommend calling Pertronix with any unanswered questions you might have. They are happy to help, and know their products better than we do

 

[DanielW]

If you don't own a front mount N, you might not understand why that's a big deal.

Very true - I can certainly understand. Whoever came up with that front-mount dizzy location had a twisted sense of humour. If putting a Pertoronix kit in mine meant I never have to touch it again, I'd definitely go for it. For me however, it's rather that I've found electronic kits to be more temperamental/problematic than points/condensers. But maybe I've just been lucky.

 

[dbsoundman]

Great info so far, thanks guys! It occurred to me I’m probably measuring the coil resistance incorrectly. I metered across the spring contact and the “tongue” contact on the bottom of the coil. Should I be measuring from the top wire terminal to one of the two contacts on the bottom instead?

Also, related question: if I have a “12 volt coil” purchased new, do I still need a ballast resistor? I bought one for my 9N and also replaced the ballast resistor but now I’m questioning whether or not it really needs the resistor. The 9N has traditional points and condenser.

 

[DanielW]

Great info so far, thanks guys! It occurred to me I’m probably measuring the coil resistance incorrectly. I metered across the spring contact and the “tongue” contact on the bottom of the coil. Should I be measuring from the top wire terminal to one of the two contacts on the bottom instead?

Also, related question: if I have a “12 volt coil” purchased new, do I still need a ballast resistor? I bought one for my 9N and also replaced the ballast resistor but now I’m questioning whether or not it really needs the resistor.

If it's a 12V coil, it will have around 3 ohms internal resistance and thus you shouldn't need any ballast resistor. Measure from top post to bottom spring to get the reading for the primary side.

Edit: I know I'll probably catch heck for saying that. A lot of folks swear the original resistor is needed no matter what. Ultimately, it will likely run fine either with or without the stock resistor if you have a 12V coil. The only reason for keeping the stock resistor with a 12V square-can coil is because a lot of the aftermarket front-mount coils are pretty lousy and don't always last. Dropping the voltage through the stock resistor helps them last a little longer if they're of cheaper quality. Ultimately: Really shouldn't make any difference either way in a basic 12V conversion that still uses points/condensers. It's not like there's any magic to the N system compared to any other 6 or 12V system. The only curveball is the wacky square coils: Many of the aftermarket ones (both 6V and 12V) aren't great quality, and all of the 6V ones (both factory and aftermarket) need a little more combined resistance than other 6V coils. With any 12V coil you'll usually find there's usually not enough resistance in the stock N resistor to make a difference in how it runs either way. If your other 9N with its 12V coil and points/condenser is running fine with the factory resistor, you might as well keep it in there. But in your 8N with a Pertronix kit, you want to listen to Non-farmer and remove all resistors. In my (admittedly limited) experience working with electronic modules, the electronic kits will also usually run with a resistor in-line with the 12V coil. But you absolutely have to make sure the power wire that goes to the module gets full voltage with no resistor. This was the mistake on a co-worker's Case 430 I helped him with a while ago. He hooked the power wire for the module to the input side of the coil. But he also had a ballast resistor running to the coil (because it was a 6V coil). This meant the power wire to the Pertronix module was getting less than the full 12V.

 

[Jim.ME]

It has been discussed here over the years, and it appears the square 12-volt coils for the front mount distributors only have about 2.5 ohms resistance. They were designed to use with the original resistor behind the dash, no second ballast resistor. As far as if Pertronix wants that OEM resistor to go away, that is a question you should ask them to eliminate any issues later.

Your 8K ohm reading does not sound like you were checking the resistance of the primary circuit which is the power in terminal to the ground terminal of the coil, not to the secondary high energy discharge terminal of the coil.

 

[Hobo,NC]

Hi all, I recently picked up what I believe to be a 49 8N (front mount distributor) that has a Pertronix conversion kit in the distributor, and the tractor was also converted to 12 volt, albeit a little sloppily. When I first tried to get it running, I couldn't get the starter to move unless I hooked it straight to the battery, so I knew the battery ground connection was no good. Today, I cleaned up that connection and the starter sounds good, and I'm getting 12 volts at the coil, but no spark whatsoever.

Now, I traced through the wiring, and I did see that someone bypassed the ballast resistor entirely, so the coil is fed directly from one side of the ammeter up front. I did see the extra wire coming out of the distributor from the Pertronix control unit which goes up to the top of the coil, so it also gets fed 12 volts. I took off the distributor and looked everything over and gave it a cleaning, and it looks perfectly fine. I used both a spark plug test light and tried laying a plug out by the block, and in both cases I got absolutely zero spark.

Given that I've never worked with the Pertronix, I have a few questions:

First, I read on the Pertronix site that the ground resistance from the aluminum mounting plate of the control unit to the battery negative terminal should be 0.2 ohms or less. I measured mine after cleaning things up and I was seeing between 0.3 and 0.4 ohms. Is that really too much ground resistance?

Second, I'm not clear if I should or should not have a ballast resistor connected. I got the impression from some parts sellers that a ballast resistor was required for any 12 volt coil, but I'm not sure that's true.

Finally, along with this tractor I got several boxes of parts including a complete distributor and coil, but the coil has a broken screw on the top for the wiring. I compared the resistance of the Pertronix coil (or at least the one that came with the setup- the label is not legible and it has no markings) with the other coil I have which is marked "Ford", and both measured something like 8k ohms. Is that indicative of a good coil?

Overall I'm wondering if the bad ground situation fried the Pertronix unit. I'd like to try slapping the old distributor back on it once I add the resistor back in but I really wanted to know if the mystery gray coil that is currently on the tractor will work with a traditional distributor, or if it's a specific Pertronix coil.

1) On all front mount coils 6 are 12 I use the OEM resistor, positive are negative ground and EI all square can coils get the resistor.

2( points and EI suffer from the same issues

3) get rid of the square can coil and all the problematic connections and use a external round can coil life will be good.

Thread 'Bob's Front Mount External Coil conversion'

Feb 22, 2019

Bob does this get a passing grade...

I kept waiting for a used cap to fall in my lap could not wait any longer so cut up a good 8N side mount cap for the coil tower... I had about a hour to 1-1/2 in my first one... I have about 6/7 layers of fiberglass on it my thinking was to add a little support to the coil tower...

• Hobo,NC
• Replies: 36
• Forum: Ford 9N, 2N & 8N

 

[dbsoundman]

1) On all front mount coils 6 are 12 I use the OEM resistor, positive are negative ground and EI all square can coils get the resistor.

2( points and EI suffer from the same issues

3) get rid of the square can coil and all the problematic connections and use a external round can coil life will be good.

Thread 'Bob's Front Mount External Coil conversion'

Feb 22, 2019

Bob does this get a passing grade...

I kept waiting for a used cap to fall in my lap could not wait any longer so cut up a good 8N side mount cap for the coil tower... I had about a hour to 1-1/2 in my first one... I have about 6/7 layers of fiberglass on it my thinking was to add a little support to the coil tower...

• Hobo,NC
• Replies: 36
• Forum: Ford 9N, 2N & 8N

Very cool! But what happens when that cap gets worn out? More fiberglass work?