If there is any ignition component that gets an unfairly bad rap, it’s the coil. Coils are very quickly blamed for ignition problems, yet almost universally they are not at fault. Coil manufacturers must love this, however, as it sells a lot of coils.
We discussed the theory behind an ignition system in our last issue, and now it’s time …
You should also test the spark plug wires. 0- 5000 Ohms is a good range for the plug wires to operate within. Anything above 5000 Ohms per wire will stress the coil and force other failures in the HT (10kV+)system. They can even lead to misfires which can destroy an electronic ignition or a condenser in the LT (12V) triggering system.
You're correct about the coil and starting problems but if the car does start the coil can still be bad.I was having a problem with my 68 Cortina GT.Start fine and idle but driveability not right.Hard to pull out on hills or even slight grades.Would have a miss about 3500rpm's sometimes.Sluggish on hills et.Checked timing,plugs wires all fine.Tried some re jetting of the twin Webers...nothing changed.Then one day when it starting missed I looked at the tack and it was going crazy.Needle bouncing all over the face.Electrical I thought....but what.Then i remembered what a local drag racer told me about his cars issue.Was using a Pertronix coil about 3yrs old.Changed to a very old...25yrs at least...Lucas Spot coil I had on the shelf...problem solved.All the issues mentioned above gone.Runs like she should now...So that Pertronix went in the trash.Had the same on the other Cortina so changed that to a new Lucas one just in case it failed sometime.So in my case a duff coil was the performance/driveabilty problem.Sorry for the long post...
Cannot believe the Condenser wasn't mentioned! If you are still running points and a condenser, replace the condenser first. Much cheaper than a coil!
In reply to Vintageant :Used to carry a spare set of points/condenser back in the past.Especially since my Cortina had a Ford dist.that ate condensors.Now with Lucas dist in both I use Pertronix ignitor's.
Recently returning to UK from Florida with my trusty TR6 , wouldn't start after standing in damp/cold for a couple of weeks even though it had been running sweetly previously.
Before pulling everything apart I remembered previous UK experience and removed distributor cap, sprayed inside liberally with WD40, sprayed HT leads and plug caps.
Fired up straight away.
Condensation in engine compartment often an easy fix in cold damp climates !
Good article, with simple tips.
I remember visiting Jamaica in the 2000's and on my travels one day, I saw a family standing around their car with hood open. I pulled over to assist, they said car won't start, just quit. First, I asked do you have fuel in the car and they said, yes. Secondly, I did my spark test, no spark at plugs, then off to the distributer. Popped the distributer off and the rotor had somehow split, where it connects to the shaft, problem solved (rotor had fallen off, firts time I saw that issue).
I had an interesting ignition failure several years ago. I was driving my car when the engine died with no warning. I coasted to a stop and took a look in the engine compartment. I found a spark plug lead had come off the distributor and put it back on. I didn't expect that to fix the problem and it didn't.
I had the car towed to a friend's house (I was 800 miles from home) and set about diagnosing the car. The engine was getting fuel. There was what looked like a good spark at all four plugs. The timing was correct.
On the third day of working on the car, a bunch of friends were over helping and it was starting to get dark. I was trying to start the car when someone noticed arc'ing on the side of the block. On this engine, the coil is at the front of the block and the distributor is driven by the rear of the intake cam, so the coil lead runs along the block between the two.
I took a look at the coil lead and there was a pin hole on its side where the arcing was observed. I put a piece of electrical tape over the pin hole, tried to start the engine, and it fired right up.
how do you bench test a coil ?
I had a new very early first year Jetta, 1980 I think. After not very many miles it startred running rough. A bit of troubleshooting found that the points were burned. Filed them a bit to get home. Replaced by the dealer, they burned again. OK, so what's going on? I opened the distributor and poked around, wanting to find something to blame. The cap and rotor looked OK, plug wires ok, the wiring to the coil was ok, but suddenly I realized what it might be. No internet in those days, so at the VW dealer, I asked the service manager what the square thing on the side of the distributor was. The condensor for the points, he replied. OK, so what's the cylindrical thing inside the distributor? He popped the hood, opened the distributor. Oh my, or words to that effect. Somehow the early Jettas ended up with two condensors of the proper value, both wired into the circuit. That can damage the points just as bad as no condensor. He clipped the lead on the external condensor, no more problems.
In reply to Carl Heideman :
My favorite item is a pen like tester. Lay it on a plug wire and if the window glows the plug is firing. Fastest way to check all 12 plugs/ wires. 
One more uncommon failure
BMW early m30 with classic distib, points, condensor, mech and vac advance.
Another HPDE driver's car....all was fine, suddenly the engine died..."Like I turned off the ignition switch". Further questioning...failed when lifting foot off throttle.
Small braided wire that connects rotating plate with points mounted on it to ground of the distributor frame....broke with the movement caused by low-to-high vacuum.
Quick trackside fix. New friend!
Pretty easy to diagnose a bad coil.
The instructions are in every automotive textbook ever written.
Thank you for a very comprehensive straightforward guide to determine why there is no spark.
I had inadvertently wired the ignition & distributor wires wrongly to the coil.
It resulted in the fine copper wire connecting the LT terminal on the distributor to the contact breaker, burning out.
Previously spent half a day without success. Your guide led me straight to the fault.
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