Diagnosing our Triumph Spitfire’s ignition issues

We’ve all been there. We looked under the hood of our 1973 Triumph Spitfire and found a mishmash of ignition components from different eras. 

We purchased the Triumph partially disassembled, as the previous owner had rewired the car and moved on to rebuilding the fuel system before passing away. Once we reassembled the fuel system and tried to start the car, it was clear we needed to go back to basics.

Initially, the engine would start and then immediately die. After some time with a test light, we found the problem: The coil was getting power during cranking but losing it once the key was turned back from “start” to “on.”

Our Spitfire was originally fitted with a ballast resistor, meaning it had two distinct circuits for coil power. The first one went straight from the battery, through the ignition switch and then onto the coil. This circuit provided full voltage during cranking. 

The car’s second circuit ran from the battery to the ignition switch, then to a ballast resistor before reaching the coil. This circuit provided less voltage to power the coil while the engine was running in order to reduce wear on components.

Our Spitfire’s ballast resistor, as well as the entire circuit that contained it, was simply gone. We’re assuming the previous owner deleted it without realizing the implications. This was not a good sign for the rest of the system; we had no idea what demons might be lurking inside. 

We faced a decision: Restore or upgrade? 

PerTronix Ignition sells retrofit kits to bring modern technology to old cars like ours, making it easy to delete the points and/or upgrade to a higher-output coil. One of the company’s most popular products, the Ignitor, simply replaces the stock ignition points, converting a mechanical switch to an electrical one. Ignitors don’t need a ballast resistor, which is why we’re assuming the previous owner deleted ours.

After some further investigation, we found an Ignitor in our Spitfire’s distributor as well as a shiny new ignition coil. Clearly an electronic conversion was in the works, and a few wires were mixed up. No big deal, so we charted a course: We’d fix and upgrade our ignition system to be fully electronic. 

The culprit behind drivability issues with our Triumph Spitfire? The wrong coil paired with our PerTronix Ignitor. Swapping in the correct coil–and having a basic understanding of how ignitions work–solved everything.

We added a circuit to power the coil with full voltage when the key was on but not cranking. Finally, our Spitfire was a running, driving car. Briefly. 

After only a few minutes of driving, the engine began randomly cutting out. Clearly we still had work to do. To rule out any issues, we went back to basics, installing a set of points and a condenser after confirming our coil was good. 

If points solved the problem, we would know our issue was in the coil control system and could diagnose from there. Luckily, they did, meaning it was time to figure out what was up with our electronic ignition system.

So we talked to PerTronix, which has a whole department of support personnel to answer questions just like ours. As the company’s own Andy Lee explained, it’s common for projects like this to have a whole mess of mismatched components–components that need to play well with each other to make a complicated, old-fashioned ignition system work. PerTronix sells three different Ignitors–the Ignitor I, Ignitor II and Ignitor III–and besides offering different features, they also have different ignition primary circuit resistance requirements. 

Which leads us to the solution to our Spitfire’s problem: That shiny new ignition coil was incorrectly matched to its shiny new Ignitor II. After swapping to a PerTronix Flame-Thrower II coil, our Spitfire finally runs correctly. 

So what did we learn? While our Spitfire’s ignition problem turned out to be a simple fix, we would have never found it without fully understanding the system we were working on–and, perhaps, without a helpful phone call. 

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