Search For Used Cars

THE MYSTERY OF CLASSIC CAR ELECTRICS

THE MYSTERY OF CLASSIC CAR ELECTRICS

Posted by Glenn Rowswell on 10th August 2017

Just when you think you have car electrics figured out, there’s a problem that comes along that you just can’t solve, as Ted Connolly discovers…

Electrics flummox a lot of classic car enthusiasts. They are quite capable of rebuilding engines, sorting out bodywork and so on, but when it comes to wiring and the various electrical components, they are stumped. I suppose the main reason is that electricity is an elusive commodity because you can’t see it, feel it, touch it, taste it or even smell it. Yeah, okay, I know there are a few wise guys out there who say that it communicates with each of your five senses and I’m a dimwit (a point I probably wouldn’t dispute, to a large degree), but electricity is entirely intangible and invisible. What you can see, hear, taste, touch and smell is the result of electricity – such as a spark, burnt wire or, indeed, a motor turning. You cannot actually get hold of a lump of electricity, enjoy its fragrance or give it a chew.

Anyway, this is getting a bit complex for my feeble brain and probably a touch boring for yours. But the point I am making is that many people do not understand electrics and would rather leave them to a relative expert.

However, although no expert, I’ve always been pretty good at wiring and its associated components, to the extent that over the years, a lot of car-owning mates have asked me to fix this and that.

It’s always seemed logical to me; power has to go into a wire and come out the other end. You can check that with a meter or even a bulb and a couple of bits of flex. If the power isn’t going in, you have partly isolated the problem. If power isn’t coming out then you know the circuit is at fault. If it is then the component it’s supposed to be operating needs attention.

However, there was one particular occasion when I was completely defeated (well, there had to be, otherwise a greater part of this page would be blank).

It was a proud moment when I bought a Cooper S. That is, the real thing and not the modern pretender (as good as it undoubtedly is). This was a long way back when the 1275S was a really cool car. However, for some reason, the factory never fitted a rev-counter, which was rather remiss because not only was it something you’d expected with a car of such pretensions, but it also added to the ambience of the cockpit. Certainly, I was aware that the engine could easily reach (and probably exceed) 7000rpm, which was a lot for an A Series lump and it was something that needed to be monitored.

Car accessory shops were different back then and stocked all manner of stuff, such as lumpy cams, big-bore exhausts, suspension lowering kits, gas-flowed heads and all of that palaver. There was a strong market for such equipment, because cars were so basic to start with compared with today’s jalopies, which have just about every gadget you could wish for as standard. Thus, there was also a huge choice of aftermarket gauges which, of course, included rev-counters.

I chose a big, black one with orange lettering and needle (yes, I know, flash little blighter) and spent a thoroughly enjoyable morning bolting it to the dash and wiring it up. As soon as the engine was running, it showed about 2500rpm at tickover and then proceeded to read at least 2000rpm too high throughout the rev range. The instrument was apparently at fault, so I took it back to the shop and, after a bit of negotiating, they agreed to exchange it.

The replacement behaved exactly the same, so the fault lay with the car. I checked and rechecked the wiring. It was exactly as it should be, according to the fitting instructions. So what was the deal? Well, I’d run out of ideas, so I consulted a friend who just happened to be a factory-trained Rolls-Royce mechanic (today, you’d call him a technician, back then, I called him a dashed handy bloke to know).

It took him a while, but he eventually figured out the problem. Have you any ideas? Of course not, and even if you have, it wouldn’t do any good because I flogged the car more than 30 years ago. Anyway, back to sense and a flippancy-free world. He sussed out that the coil was wired back to front. In other words, the live wire from the ignition was wired to the positive terminal and the wire to the points was connected to the negative spade. Since it was a positive-earth system, it should have been the other way round. The rev-counter was connected to the coil and worked by counting the power pulses. However, as soon as the ignition was switched on, the tacho was getting a constant live – which pumped up the reading – and it fell on each firing stroke, when there was a brief lull in the power. I know I haven’t explained that very well, but I’m hoping you get the idea that instead of the needle being pushed up by the power pulses, it was falsely high to begin with and actually fell on each firing stroke.

Anyhow, even if that’s too poorly explained to comprehend, you will understand that it was all down to the coil being wired back to front. I didn’t know, until then, that a coil would run backwards. Apparently, it works at a reduced voltage and efficiency is decreased, although I never noticed the difference before or after.

You learn something new every day, eh? Such as that the ohm was named after German physicist Georg Simon Ohm, the ampere was named after French physicist André-Marie Ampère and the volt takes its name from Italian physicist Alessandro Volta. Or that Wikipedia can sure make you sound intelligent.