lucas amps guageIn this blog I’m going to talk about the merits of upgrading from an older positive earth dynamo system to a negative earth alternator…

So in the ongoing quest to maintain power, some hold this demeanor with their interactions with others, some strive for this under the bonnet of their beloved motor car.

I can’t tell you how to become all Tony Montana aka Scarface who was obsessed with gaining “the power”…but perhaps I can help you in the motoring department.

I’m not talking BHP here either, I’m talking volts. One of the most over looked and under estimated components when it comes to causing gremlins is the car’s battery itself, especially on newer cars.

The first generation Jaguar XK8 and 90’s Bentley Turbo R for example are very sensitive to the condition of their battery, this should always be the first thing to check when warning lights appear. Disconnect the battery, charge it up and watch the lights go out if there are no underlying faults – this is called a hard reset. Just remember your radio code, wouldn’t want to miss The Archers now would you? If in doubt, a new battery is never a bad idea, most have warranties so do keep the receipt.

A common misconception is that batteries die from lack of use of the car, although there is a fair bit of truth to this, I found it was change in weather that killed batteries – so keep an eye as the cold snap sets in.

We take for granted that modern cars tell us if there is a problem with the charging system and the clever alternator does all the thinking for us. With classic cars however, you have to look a little closer…especially if your beauty is equipped with a dynamo.

A magician I hear you ask? …no…

Have you a gauge on the dash with ‘C’ and ‘D’, and the needle swings towards ‘C’ as you rev the engine? If so you do indeed have a dynamo, and from my experience this charging system requires a battery being in tip top condition to begin with and subsequently relies on the driver raising the engine speed to keep the charge rate up when you have the lights, wipers and interior fans on. If not the battery begins to lose charge and the car starts to die until you cannot restart it.

The battery guage’s ‘C’ stands for charge and ‘D’ for drain – nice and clear.

There is nothing wrong with this sort of system, but replacing your dynamo with an alternator kit will not only release you from the stress of keeping an eye on charge but also gives the engine crisper cleaner power due to a stronger more consistent voltage supply to the coil and in turn bigger sparks at the plugs. So there is more to be had from this “suck squeeze bang blow” process.

suck squeeze bang blow

Having experienced this swap on a Jaguar E Type series 1, I can hand-on-heart say the car felt more alive, carrying the booster pack around was no longer necessary and the car always started easier. Please be mindful some cars must have the polarity changed from positive earth to negative, but it goes without saying that a skilled auto electrician must carry out the conversion.

We all like to buy our mechanical pets presents from time to time, and the really satisfying spend is when your hard earned improves the car too, so with Christmas close by, why not check out that alternator kit if you are running with a dynamo!


Mike Atwall
This article was written and published by Mike Atwall. Mike works for Trade Classics as an in-house journalist and copywriter and has many years’ experience in the classic car sector – for over 8 years he was the General Manager of the Classic Car Club in London and responsible for a fleet of over 100 cars worth multi-million pounds. So there’s not much Mike doesn’t know about makes, models, maintenance and idiosyncrasies of these old cars. Mike’s a true petrol head with a deep passion for the classics and he loves to talk cars all day, so why not write a reply on this article below.

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