How does the Weasley's car run?

Question

Mr. Weasley puts a charm on the car to make it bigger on the inside.

Mr. Weasley has used this charm on his flying car, which we see in Harry Potter and the Chamber of Secrets, to make the inside of the car larger than the outside.

source: Wikibooks Muggle's Guide to Harry Potter: Undetectable Extension Charm

However, we learn that electricity doesn't work around magic.

Magic was known to interfere with the functionality of Muggle technologies powered by electricity.

source: HP Wikia: Electricity

How can anyone drive the car if electricity won't work?

Answer 1

The very short answer is that cars work perfectly well around wizards.

Quoting from Pottermore's page on "Technology" (as written by JKR herself)

There is one major exception to the general magical aversion to Muggle technology, and that is the car (and, to a lesser extent, motorbikes and trains). Prior to the introduction of the International Statute of Secrecy, wizards and Muggles used the same kind of everyday transport: horse-drawn carts and sailing ships among them. The magical community was forced to abandon horse-drawn vehicles when they became glaringly outmoded.

It is pointless to deny that wizardkind looked with great envy upon the speedy and comfortable automobiles that began filling the roads in the twentieth century, and eventually even the Ministry of Magic bought a fleet of cars, modifying them with various useful charms and enjoying them very much indeed. Many wizards love cars with a child-like passion, and there have been cases of pure-bloods who claim never to touch a Muggle artefact, and yet are discovered to have a flying Rolls Royce in their garage. However, the most extreme anti-Muggles eschew all motorised transport; Sirius Black's love of motorbikes incensed his hard-line parents.

Answer 2

• Very simply, there's no canon contradiction. Your second source (Wikia) is, as usual, wrong^[1], in a very typical - for Wikia - way.

  1. They take a very specific known canon fact (electronic surveillance bugs don't work in Hogwarts due to excessive magic concentration)

  2. Then they make a wholly unjustified leap using a logical fallacy (Hasty generalization or some other inductive fallacy), falsely deducing that any magic causes electricity around it not to work.

  In reality, electricity works fine around some magic, for example:

  • Wizards don't cause massive electrical outages around them when they do magic around Britain in general.

    We know that massive concentrations of magical activity are all around Muggles: MoM is in the middle of London. 12 Grimmauld Place is too. Diagon Alley is too.

  • Knight Bus runs all around Muggle streets without shorting out any electricity or shutting down any cars around.

  • Harry's house's electricity worked perfectly fine when he or Dobby performed magic around the house.

  • King's Cross train station - where Muggle trains presumably work on electricity - works perfectly fine despite Platform 9 3/4 and Hogwarts Express being around.

  • For that matter, Ford Anglia of Weasley's infamy drove around Muggle roads without affecting Muggle cars:

    Harry couldn't see how eight people, six large trunks, two owls and a rat were going to fit into one small Ford Anglia. He had reckoned, of course, without the special features which Mr Weasley had added.
    ...
    'No one would see. This little button here is an Invisibility Booster I installed – that'd get us up in the air – then we fly above the clouds. We'd be there in ten minutes and no one would be any the wiser...'
    'I said no, Arthur, not in broad daylight.'

  • Dumbledore explicitly needed Deluminator to shut down streetlights - as opposed to just casting a random spell around them.

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• Leaving that aside, I'm pretty sure that wizards could have easily made a self-propelled car using magic.

  • You don't necessarily need spark plugs and a battery to ignite the fuel in car engine when you have numerous spells to create sparks (and 1960 Ford Anglia doesn't need electricity for anything else, no onboard computer as far as I know).

  • You don't even need an internal combustion engine, since you can propel things using magic - they have been building flying apparatuses well before electricity (flying carpets, brooms, later flying carriages).

    Matter of fact, Weasley's Anglia ran around the Forbidden forest, unsupervised, for months, in CoS. I suspect it may not have needed gas because of that, so it probably didn't run off of ICE.

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_{[1] - Among experts here, Wikia (especially Harry Potter Wikia) has reputation of being notoriously inaccurate, unless they cite an exact source and quote to back up what they are saying. They have an unfortunate tendency to engage in either logical fallacies like the one you stumbled into (inductive fallacy, extrapolating one fact into a non-existent pattern), or trying to write a story narrative to explain a specific canon fact (the narrative not being suppoted by canon).}