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Haynes’ World: Triumph’s under-bonnet wiring woes cured

Haynes World Spitfire

Haynes' World is a regular feature that takes a look at what the staff at Haynes are doing with their cars, bikes and other vehicles. This time, product manager Nigel Donnelly and his Triumph Spitfire Mk4.

Triumph Spitfire maintenance

Car: 1972 Triumph Spitfire Mk4

Owner: Nigel Donnelly, digital product manager

A Triumph Spitfire is not a complex vehicle, but its age means there are a lot of things that are not quite as they left the factory.

In the case of this particular car, it left the factory in Sienna Brown, rather than the bright white it now wears. It also has a glass fibre boot lid and the ignition system has plainly been mucked about with. It runs ok, but does not turn off when the key is turned off.

Paint colours and plastic body panels are one thing but electrical oddities give me the fear that I will end up scratching my head at the side of the road and have no idea how to get things going again. So I broke out the multimeter and started looking for electronic ghosts in this elderly machine.

Haynes Manual Triumph Spitfire

The Haynes Manual for the Triumph Spitfire is still very much available so I got myself a digital version, zoomed in on the wiring diagram and printed it out to allow me to see if there were any anomalies.

All the connections to the ignition switch were connected correctly and the switch was doing its job, so the next step was the ignition system itself. 

As mentioned previously, the ignition system is modified from the original set-up. The manual showed an early Mk4 Spitfire such as mine should have a ballast resistor ignition set-up and I could see there wasn’t one present.

As owners of old Triumphs will remember, access to the engine bay on Spitfires, GT6s, Heralds and Vitesse models is peerless and I was able to sit on the nearside wheel as I poked and prodded at the various components. 

I did, however, have a nasty little homemade cable between the solenoid and the coil (shown below). Removing this meant the car would not start. Having it in place meant the car would not turn off. It needed investigating. 

As you can see here, a green cable was connected to the positive side of the coil. A white cable ran from the other side to the distributor. In order to run, a temporary cable from the solenoid was run to the positive side. None of this resembled what I would expect to see in the wiring diagram.

Given that the swap from ballast resistor to non-ballast ignition means a change of coil, my first task was to see what coil was fitted.

Looking at the label, I could see it was a 12v coil, which is the correct type for a non-ballast system. Using the multimeter confirmed this. It measured a resistance of around 3 ohm. A resistance rating of around 1.5 ohm would indicate a ballast-resistor coil was in use.

Spitfire electrics

Now the task was to wire up the coil correctly (as shown below). The temporary red cable was binned. The green cable, according to the wiring diagram was wildly out of place. It appeared to be for the reversing light switch and I suspected it had been poked onto the coil as it looked like the right place. This was removed, which meant we needed to find a power supply for the coil.  

When the car left the factory, there would have been a white cable to one side of a ballast resistor and a yellow/white one out of the other side connected to the coil. Without the resistor, you need to connect the white wire directly to the coil and you can safely stow the yellow/white one because it’s no longer required. 

The white cable was too short to reach the coil, but I rigged up a temporary cable to see if connecting things this way allowed the engine to start and stop on the key. 

Triumph Spitfire ignition

Success! Now the engine stops and starts on the key, but a new symptom has emerged. We now have no fuel or temperature gauge, both of which worked previously.

A Triumph Spitfire may not be a complex vehicle, but I suspect I won’t be putting my multimeter away just yet.