Category: Ignition

Tech Tip: Ignition Coil Polarity Check on Early Model Vehicles – Randy Rundle @Underhood Service

Tech Tip: Ignition Coil Polarity Check on Early Model Vehicles – Randy Rundle @Underhood Service


Rundle’s Rules: Ignition Coil Polarity Check

Prior to 1956, the year when most all of the domestic auto manufacturers upgraded to 12-volt electrical systems using standardized negative ground designs, some of the electrical systems on cars and trucks were positive ground and some were negative ground.

Ford used positive ground, while General Motors used both.

Chevy trucks were negative ground, while GMC trucks used positive ground. There was and still is a lot of confusion concerning the polarity of electrical systems and how to properly connect the ignition coils, as well as the battery.

On classic and antique vehicles, you can test for correct polarity of the ignition coil by using a voltmeter.

Connect the negative lead to the (-) negative terminal and the positive lead to the engine block.
Set the meter on the highest volt range (these connections are the same whether you have a positive ground or negative ground electrical system).

The secondary winding’s polarity, which you are testing, is determined by the combined hookup of the battery and primary windings.

Crank the engine over (do not start it) and the needle of the voltmeter should show an upward swing to the plus or positive side (don’t worry about taking a reading).

If the needle swings down to the negative side and gives a negative reading, your coil is hooked up backward. To correct the polarity, simply reverse the coil primary leads.

A coil with reversed polarity will have about a 20% lower output, which may not show up at idle and low rpms, but can cause an engine to miss or stumble under load and at higher engine rpms.

This is why a technician who changes the points, condenser and other electrical components will still detect an engine miss.

The lesson here is, too often, it is “assumed” that the wiring is correct.

— Randy Rundle

Randy Rundle is the owner of Fifth Avenue Antique Auto Parts, Clay Center, KS, and services antique and classic vehicles. An author of six automotive technical books, Rundle has spent 20-plus years solving electrical, cooling and fuel-related problems on all types of antique and classic vehicles.

Magneto or distributor: which do you choose? – Chris Reed


This article is from a tractor website but the question is valid when you are building an early hot rod

Magneto or distributor: which do you choose?

A defining trait of the antique tractor is its lack of a conventional battery. One of the first things to know when trouble shooting, restoring or buying, is where its power comes from – is there a battery or not?

At one point, the answer was probably as simple as checking a model, date or serial number. But since so many machines have been modified to convert from magnetos to distributors, those methods might be a little out of date today. Nevertheless, understanding where your tractor’s power comes from is critical to knowing which replacement parts to buy – and to decide if converting to a different power style is worthwhile.

To review, every gas-powered engine needs two essential things to start, a spark and fuel. The spark fires the spark plugs in rhythm, igniting the gas in the combustion chamber. The question as it relates to this post is where that spark comes from.

The main difference between a magneto and a distributor is that a mag is self-contained & DOESN’T need a battery to produce a spark. A distributor, on the other hand, requires an external power source to operate.

Magneto technology has been around for a long time. The unit is essentially a distributor with a generator built in – it still has a coil, it still has a set of points and condenser and it still has a spark rotor and distributor cap. When tractors first came into being, batteries were not part of the picture, so operators needed to hand crank a generator, which then provided power to the tractor.

Magnetos have proven to be a reliable way to run a tractor, and a well-built magneto can produce a similar amount of spark compared to an electrical system. They also have been, historically, easier to come by. In fact, during World War II, tractors that were originally built to be battery powered were switched back to magneto technology due to battery shortages.

(Of note, magnetos can work in conjunction with batteries as well, providing self-produced power to the tractor when the battery dies, but does not require one).

Of course, this is not to say that battery-powered systems don’t have their advantages. Nothing beats the convenience of electric start and most distributors simply produce a stronger spark than magnetos. In addition, distributors can give you the extra power needed to run auxiliaries such as headlights. They are also, generally, easier to maintain and understand for most people.

An alternator is also, then, required to re-charge the battery in an electrical system.

What do you prefer on your tractors? Do you use a magneto, or is yours battery-powered? Have you thought about converting? Tell us below.

New Paris can be found here

Lightning makers: Five things to know about spark plugs – David Conwill @Hemmings


What we call a gasoline engine is a species within the internal-combustion engine genus that doesn’t actually have to use gasoline (see: propane, alcohol, nitromethane, etc.). What really sets it apart is its ignition system, using electrical spark gaps to light off the fuel-air mixture. Various parts of the spark-ignition engine have changed over time, but one constant, since before the American Civil War, is the spark plug.

That’s not to say spark plugs haven’t changed since 1860. Like most things automotive, they reached their most familiar form in the 1930s and have been continually refined in detail ever since. Because of their long history, there’s a lot of information floating around out there about spark plugs that may or may not be relevant to your classic car.

Talking about spark plugs must, of necessity, be done in generalities. There are a lot of ignition products on the market and many of them are excellent. Nomenclature especially varies from brand to brand. Thus, one maker’s heat ranges may run from hot to cold with the numbers going down as a plug gets colder, while another may do the opposite.

Plug selection should be tailored to the conditions under which your engine will be run. A car that putters through the occasional parade will demand a much different plug than a similar car called on to haul a load of passengers to a scenic overlook. Our hope with this piece is to arm you with the knowledge so you can do your own research when choosing your next set of spark plugs.

1. Parts of a plug

Viewed externally, the spark plug is a pretty simple device, made of metal and porcelainized ceramic. The ceramic part, called the insulator, is formed from sintered aluminum oxide. The insulator keeps the ignition spark from shorting against the cylinder head. At the upstream end of the insulator, nearest the coil, is the terminal. This is where the spark-plug wire terminates. Various attachment configurations exist. Most modern cars use snap-on wires with rubber boots, but earlier cars used a nut to hold a bare eyelet onto the terminal. The terminal connects through the center of the insulator to the central electrode. Once at the central electrode, current from the coil jumps to the side (aka lateral) electrode. The side electrode is attached to the jacket (aka the case or shell), which is the metal part that screws into the cylinder head.

Read on

D&B Quick Point Gap Setter for Model A Ford


The “Quick Point Gap Setter” tool is a very simple way to solve an awkward challenge.

Some may say it’s a lazy way out, but for me it makes the operation so simple it’s a no brainer particulary when out on the road.


First remove the distributor cap, rotor and the distributor body to gain access to the breaker points. Always
inspect the contacts to see that the surfaces are not burnt or pitted. If replacement of the point arm is required,
refer to Les Andrews’ “Mechanics Handbook” to replace the original style point sets. The newer “Modern”*
point sets are replaceable without removing the distributor cam and upper plate. Once the new arm is in place
and the cam is reattached, set the points using this tool.
1. Loosen the clamp screw on the top of the fixed point block (on original style points), on modern points
loosen point mounting screws.
2. Remove the rubber stopper from the tool and set it aside.
3. Manually open the points sufficiently to slide the Cylinder (the Shell) of the tool over the cam so that the
sleeve covers the cam lobes.
4. Release the move-able point arm so that the rubbing block of the move-able point arm rests on the
outside of the sleeve.
5. Use the thickness gauge that projects from the rubber stopper to gauge the gap between the fixed
contact and the move-able contact.
6. Once you have achieved this setting, tighten the clamp sleeve on the fixed contact (original style), or
modern points tighten the mounting screws, and remove the cylinder from the cam.
7. Place the stop

2000 Chevrolet S10 Xtreme Ignition Coil Change Part 2


Due to the horrible weather the coil change is taking longer than I’d like, but it’s getting there!

To fit the aftermarket NAPA coil the factory rivets needed to be ground down to facilitate the removal of the old unit

Once removed I tidied the ground areas up and applied some paint to stop things from rusting and make things look a little better.

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The Chevrolet S10 Xtreme Was Unwell


About two weeks ago the Chevy started to run a little rough and this had become worse ending up in a couple of breakdowns

I scanned the truck using the WiFi OBDII Wireless Dongle, using the Dash Command app on the Apple iPhone 6 Plus

No codes were found and all the diagnostics looked fine, but the truck would still stall out after about 4 miles and refuse to restart until cooled.

Luckily I had asked a friend to bring back some ignition components during a visit to the States after some previous issues, this meant I was able to swap out the coil.

(You may notice that the coil was made in Poland, so it’s had a long round trip back to Europe!!)

I have driven twelve miles in testing so far and all seems OK, I never like to have “cured” a fault without being 100%

Back to the Future (well kinda :)) Part 2


If you’ve not read part 1 please take a look here

After rewiring and getting everything put back together, the car started first time and ran beautifully, in fact the best since I’ve had it!

One thing I learned during the process was to make use of some of the tools that are available.

These two tools were really helpful


Back to the Future (well kinda :)) Part 1


After the breakdown on the way to Wheels Day 2017 and some diagnosis the Pertronix module was the culprit (well the symptom anyway :))

This is the second module failure, so it’s back to points which as least can be fixed on the road. I’ve gone for the “modern points” setup by Nu-Rex, “modern” is pretty amusing as the new plate contains the 1957 onward Ford V8 points as opposed to the original 1929 setup.

Before I began I set the timing to TDC via the timing pin as per usual on the Model A I then started to remove the Pertronix system

During removal I found that the lower distributor plate had been deleted, a bit annoying as I’d ordered the upper plate from O’Neills. Luckily John Cochran had a used item I could use (thanks John :))

I’d also ordered the recommended longer pigtail for the lower plate, this is recommended to alleviate the stress on the original which is a little short and often fails due to fatigue. So after desoldering and drilling the old pigtail was removed. Then it was a matter of a little cleaning and soldering to get the new item fitted. As my car has no pop out ignition switch I further modified the plate to securely fix the hot cable to the plate by drilling the dimple which was designed to contact the original pop out switch.

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Once all the modifications were completed I installed the plate into the distributor.

Lower plate installed

The pigtail was connected to the points contact ensuring that the connector was not able to accidentally ground to the distributor housing.

Also checked that the timing advance lever was in the fully retarded setting at this point

Next the upper plate was installed taking care to wrap the pigtail around the cam spring whilst making sure not to pinch the cable.

The upper plate will only install one way into the tabs and groove and should turn freely.

Nu-Rex Modern Points Upper Plate Installed

See the next episode for rewiring, points adjustment, timing and hopefully an engine start.