Home » You Could Steal This Car By Flipping Over The Hazard Light Switch

You Could Steal This Car By Flipping Over The Hazard Light Switch

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Older cars are generally easier to steal than new ones. They had simpler locks and simpler electronics that were easy for any garden-variety thief to bypass.  Few were quite as easy to nick as the Vauxhall Nova, however. They had a hilarious and unlikely flaw that eliminated the need for hotwiring entirely.

It all came down to the hazard switch. Pop it out, flip it over, and pop it back in. The dashboard would flick into life, and you merely needed to bump start the car to get the engine started. It was really that easy.

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On the face of it, it sounds ridiculous. How do the hazard lights help you start the car? I spent my day poring over old wiring diagrams so I could tell you all about it. Buckle up, this is a fun one!

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This is all your fault! via eBay

Yes, It Works

The Vauxhall Nova is perhaps the most well-known victim of this flaw. Built from 1982 to 1993, it was relatively popular, with over 500,000 sold, though precious few remain today. Of course, any Britlander will tell you that the Nova was really just a rebadged Opel Corsa. This trick worked on cars of both stripes with equal success, if they were duly equipped with the right version of headlight switch.

This oddball trick was historically shared amongst mates at at the pub. It was the kind of thing that sounded utterly unbelievable until somebody showed you in person. The hack eventually gained broader notoriety thanks to Top Gear. In the first episode of Season 21, the trio were taking part in one of their Cheap Car Challenges. Hammond showed up with a Vauxhall Nova SRi, the hot hatch version with a mighty 82-horsepower engine. Clarkson demonstrated the technique, flipping the switch and bump starting the Nova with ease.

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To execute the trick, you needed to gain entry into the vehicle. Once inside, the hazard switch could be pushed into the On position, which made it easy to pop out of the dash. The switch was then rotated 180 degrees and installed back into the dash upside down. If the hazard switch was still in the on position, it would provide power to the vehicle, akin to having the key in the On position. The engine could then be started via bump start, assuming the vehicle was a manual.

For a thief, using this trick meant there was no need to fiddle around and hotwire the ignition. This was somewhat of a glaring security flaw. An enterprising thief would still have to break into the vehicle and deal with the steering lock, though neither presented a great challenge on the Nova or Corsa.

Images Vauxhall Nova 1990 Dd1
The hazard switch was easy to pop out and flip over in facelift Opel Corsa and Vauxhall Nova models.

How it Works

I dived into research to figure out how this works, and it’s almost hilariously simple. The reason it’s possible at all is because of a quirk of the engineer’s design choices, combined with the fact that the hazard switch needs to work at all times, key in or key out.

The hazard switch nominally has 9 pins, though only 7 are actually populated.  The switch receives 12-volt power on two pins. On pin 6, it receives always-on power from the battery, so that it can flash the indicators even when the car is switched off. On pin 9, it receives 12-volt power switched via the ignition.

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Flip the switch, and pins 1 and 4 end up where pins 6 and 9 were supposed to go. via eBay

The trick is that when the switch is installed upside down, pins 1 and 4 of the switch mate with pins 6 and 9 of the connector. When the hazard switch is in the on position, pins 1 and 4 are connected. This bridges pins 6 and 9, such that the 12-volt battery power is connected directly to the 12-volt switched circuit of the car. This powers everything up as if the key has turned the ignition barrel to the On position.

But why are pins 1 and 4 getting bridged? I wanted to understand this on a nitty-gritty level, though, so I dived into the wiring diagrams. The first I found gave me a vague idea, but I couldn’t quite parse the archaic symbols. Eventually I learned that the same hack works on the Mk 3 Astra, which led me to a better wiring diagram that made everything clear. Notably, the switch on the Mk 3 Astra is externally different, but if you flip it around, you’ll notice the pins are in the same arrangement as on the earlier Corsa and Nova.

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The Mk 3 Astra used the same pinout on a different hazard light switch. via eBay
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via eBay
Screenshot 2024 05 21 122721
The wiring diagram of the relevant parts of the 1995 to 1998 Astra. Don’t worry – I shall explain this diagram down below!

Here’s how it works. Under normal conditions, the hazard switch is turned OFF. In this position, it provides switched ignition power to the flasher relay. This means the flasher relay only gets power when the ignition barrel is turned to On. Meanwhile, the output of the flasher relay is connected to both the indicator switch and pin 1 of the hazard switch. With the hazard switch in the OFF position, pin 1 is not connected to anything. However, the indicator switch can connect the flasher output to the left or right indicator bulbs as desired.

Pdiag1
This diagram shows the flow of 12-volt power from the ignition barrel in the on position to the flasher relay. From there, the 12-volt flasher signal goes to the indicator switch, where it can be directed to the left or right indicators. This all happens with the hazard switch in the off position.

When the hazard switch is set to ON, however, everything changes. The hazard switch now provides 12-volt power to the flasher relay directly from the battery. Thus, the flasher runs whether the ignition is on or off. As we stated previously, the output of the flasher is piped to pin 1 of the hazard switch. Now that our hazard switch is ON, pin 1 is connected to pins 4 and 7. Thus, the output of the flasher relay ends up going to pins 4 and 7, which drive the left and right indicators respectively. This leads to all the indicator bulbs flashing together.

Pdiag2
When the hazard switch is in the on position, the flasher relay is instead powered directly from the battery. The flasher output signal then travels back to the hazard switch, where it is passed to the left and right indicators at the same time.

The key detail is that the hazard switch makes a connection between pins 1 and 4 when it’s turned ON. If you install it upside down, that bridges pins 6 and 9 in the connector in the dash. That puts 12-volt battery power on the ignition On circuit in the car, which basically makes it ready to run.

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There’s no way to use the hazard switch to trigger the starter motor of course, so you’re stuck bump starting the car. Thus, this hack really only works for a manual. However, in 1980s England, a great many Novas were three-pedal jobbies, anyway.

This hack is all literally down to a chance quirk of the switch design. If the engineers had rearranged the pins on the hazard switch, this wouldn’t work. For example, if the switch was only able to be installed one way, this wouldn’t happen. Similarly, a different pin assignment would have avoided the problem.

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Sorry to say mate, your Opel’s a bit easy to nick, innit?

It’s not clear where the hack came from or who first conceived of it. Neither is it obvious at which point Opel or Vauxhall might have become aware of the problem. My research indicates that this hack should have worked on just about any Nova or Corsa with the wide rectangular hazard switch, as long as no immobilizer is fitted. For carbureted models with mechanical fuel pumps, an immobilizer on the starter circuit might not have been enough. For an EFI model, though, an immobilizer that cuts power to the fuel pump or ECU would have been enough to stop it working.

I also found one interesting forum post from someone that tried the trick on an Vauxhall Nova. The trick worked for them, though the steering lock was still a problem. They also noted the switch was hot when they pulled it back out of the dash. This would make a lot of sense. Instead of the proper ignition barrel and relay providing power to the switched 12-volt bus, it was all going through the hazard switch instead. The hazard switch would not have been designed to carry current for the entire vehicle’s systems, and so it’s no surprise it would heat up. It’s conceivable that doing this at night with the headlights on could destroy the switch in time.

Loose Ends

I like to imagine some cheesed-off engineer developed the switch this way on purpose. I doubt it, though. More likely, the switch design was optimized for easy installation and removal and engineers only later realized the problem this caused due to the pinout.

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The trick is most well known for its use in late “Mk 2” (facelifted) Vauxhall Novas and Opel Corsas built from 1990 onwards, which had the wide rectangular hazard light switch. As noted above, the trick also appears to work on Mk 3 Vauxhall Astras, which have a similar but different hazard switch design. I’ve found a forum post of someone that had success achieving the hack on that model.

The Vauxhall Cavalier falls victim to the same trick, too. Many of these models have seemingly different hazard light switches, but that’s not really the case. A great many products from Opel and Vauxhall used externally different hazard switches that had the same pin layout with the same exact flaw.

What I can’t confirm is whether or not this trick works on the original pre-facelift Vauxhall Nova or Opel Corsa. These models featured a vertical red hazard switch nestled low on the dash next to the pocket for the optional clock. I’d dearly love to know if this switch uses the same flawed pinout, but I can’t find a spare one online for the life of me.

Ear
The hazard switch on the Mk 1 Corsa and Nova was likely much harder to pull out of the dash.

It’s worth noting the reason the hack became so widely known on the Mk 2 Corsa is because it was so easy to pop the switch out and flip it over. Some videos suggest it could be done by hand, no tools required. On other cars, it may have required tools to pull the dash apart before the switch could be flipped around. This made it less relevant as an “easy” trick to steal a car, and may be why Vauxhall and Opel never changed the switch design.

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In the case of the Mk 1, even if it had the same flawed pinout, it would likely not have been such a big problem. It appears much harder to pop the switch out and flip it around. Still, it would be easier than hotwiring the car manually.

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The Mk 3 Astra had a different switch with the same pinout. However, popping it out of the dash would not be as easy as on the Mk 2 Corsa.

There is a simple way to protect a Mk 2 Nova or Corsa against this hack. An old PDF on the Internet Archive still exists from a company called Cars, Keys, and Clutch. It explains how to install a diode in line with the ignition-switched 12-volt supply going to the hazard light switch. A diode is like a one-way valve for electricity, in very simple terms. Installed properly, it allows 12-volt power to flow from the ignition barrel to the hazard light switch, so it can flow to the flasher relay and drive the indicators as needed. However, it does not allow 12-volt power to flow FROM the hazard switch back to the barrel in the event pins 6 and 9 are bridged.

Overall, this hack probably doesn’t affect you in your day-to-day life. Few of these old British cars remain on the road today. Plus, my research indicates that only 1990-1993 models are the most susceptible to this trick.

Still, if you’ve got a Mk 2 Nova or Corsa that you love like a child, be careful! Worst case, you show someone this trick at Cars and Coffee, only to see them driving off with your car fifteen minutes later …

Image credits: Opel, Vauxhall

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Mortalcombatant
Mortalcombatant
26 days ago
Daniil Ivshin
Daniil Ivshin
28 days ago

Huh, I actually have a Mk3 Astra in the garage. Might try this out.

Vetatur Fumare
Vetatur Fumare
29 days ago

We had a 1986 Opel Corsa (with the earlier hazard switch, which was not removable without taking apart the dash) but worse was our 1976 Ford Taunus GXL – my dad once locked the keys in the car and opened the door with a popsicle stick. He said it’d probably work in the ignition as well, but he didn’t want to try in case something broke.

Phuzz
Phuzz
29 days ago

But is it a real Nova if it doesn’t have a half-finished, unpainted, bodykit on it?
Also immortalised in the The Streets song “Has it Come to This?”

SR Nova, driving like a joyrider. Speeding to the corner. Your mother warned ya, it’s a sound system banger.

https://www.youtube.com/watch?v=22U2LLVRwtk

JDE
JDE
30 days ago

The Skateboard key in an early 80’s GM with the wings was pretty easy to break the lock enough to make it start.

JDE
JDE
30 days ago

the savior of these nowadays, at least it would bein the US is the number of thieves too stupid to know how to even drive a stick, much less bump start one.

Bhtooefr
Bhtooefr
30 days ago

I forget the exact details, but IIRC it’s possible to backfeed the key on circuit in an early watercooled VW even more easily – I think it’s something like, turn the headlights on, and pull back on the high beams.

Patrick Cook
Patrick Cook
24 days ago
Reply to  Bhtooefr

IIRC, it works on Mk1 Rabbits/Golfs/Jettas as well — by pulling the stalk back for high beams.

Bram Oude Elberink
Bram Oude Elberink
30 days ago

My first car was a MkI Corsa from ’88. I do not know if the hazard switch trick worked. What I do know is how annoyingly easy it was for thieves to get in the car. Probably not the only car where it worked, but because there were so many, it was an easy target; thieves tend to specialize in models. My car was broken into multiple times, each time with damage (mostly lock- and paintdamage). The first time they got in my car my precious toolkit was stolen which was hidden under the seat. From that moment on I never had anything valuable in it, even had a sign on the dashboard stating that nothing was in the car, but still then, they had to check every now and then to see if I was not lying. Simple solution would be to leave the doors open, but that would void my damage and theft insurance. Still do miss that car though..

Bram Oude Elberink
Bram Oude Elberink
30 days ago
Reply to  Lewin Day

I wonder, would thieves have a resumé, where they brag about mention their specialities. Something like: “Highly specialized in: Ford Focus, Opel Astra, Factory-radio’s, airbags.”

Morgan Thomas
Morgan Thomas
30 days ago
Reply to  Lewin Day

Probably like the bastards that broke into my work van in my driveway and stole a couple thousand $ worth of tools last Saturday night – according to the police they drive around looking for work utes and vans to steal tools from, and break windows using a screwdriver to lever against the glass in a corner to make it crack. And it was only 8 months ago that (probably the same) bastards broke into the van the same way and stole all my previous tools. Now the van gets parked at our workshop each night and my tool bags are all taken inside.

Crank Shaft
Crank Shaft
30 days ago

It sounds like you wouldn’t even need to reinstall the switch upside down. If you know which pins are which, you cold just use a jumper wire between the relative pins to power the ignition. I wonder how many other cars could be hot-wired by using the hazard light leads?

Crank Shaft
Crank Shaft
30 days ago
Reply to  Lewin Day

To avoid the switch getting hot which may be its one imperfection. :;

Mark
Mark
30 days ago

The UK keeps great statistics for car registrations. And howmanyleft.co.uk makes it searchable.
There are:

  • 220 90-2000 Novas currently Licensed today!
  • 2202 90-2000 Novas as SORN (Statutory Off Road Notification) – keep the plate active, but can’t drive, as opposed to scrap.
  • The Nova Merit has the most survivors (and semi-survivors): 63 licensed, 451 SORN
  • As far as I can tell there are zero 90-99 Opel Corsas in the UK today.
  • Comparison: there are 2621 2019 Ford Focus RS currently licensed in the UK.
Ian McClure
Ian McClure
30 days ago

I wonder if this trick is more broadly applicable, if not always as easy. Like, is it generally true that if I pried off the hazard button in an old car and shorted the right connections I could activate the ignition circuit, or is there also other unique details of harness that made this possible?

Tarragon
Tarragon
30 days ago
Reply to  Ian McClure

I had that same question as I was reading.

I have the same question for other controls that work with the key on or off. So head lights, dome light, parking lights, and I’m sure there are others.

Probably not because this requires that the component gets two sources of power, battery direct and switched ignition.

Even so I’d love to see a dome light hack to steal a car

Cryptoenologist
Cryptoenologist
30 days ago
Reply to  Tarragon

The radio harness has both switched and battery connections as well.

Someone probably realized by the mid-90s that this is a risk in a couple ways and put in diodes so that it’s not possible to back-feed. But maybe not!

Crank Shaft
Crank Shaft
30 days ago
Reply to  Ian McClure

Ninja’d! 🙂

Benjamin S Lindstrom
Benjamin S Lindstrom
30 days ago

This reminds me of the accidentally stolen Subaru in Portland, and the limited number of different key cuts Subaru used in the ’90s. So easy to steal that you don’t even know you’re doing it!

Pneumatic Tool
Pneumatic Tool
30 days ago

This calls to mind “old Fords” (like mid 70’s and earlier). Just get a long-ish screwdriver and make a bridge between the the posts on the starter solenoid relay. A few sparks, ignition, and away you go…no pesky steering wheel locks either!

ChefCJ
ChefCJ
30 days ago

I always thought this was just something silly they made up for the show. Factual Entertainment indeed

Ecsta C3PO
Ecsta C3PO
29 days ago
Reply to  Lewin Day

Well, maybe faked a little bit to overcome the steering wheel lock

Mortalcombatant
Mortalcombatant
30 days ago

Mr Day, I just wanted to say that I think your articles are very well written with a lot of research going into them and that I appreciate your work.

Greg R
Greg R
30 days ago
Reply to  Lewin Day

To add to that, are you going to be doing any rc robot stories on this site?

Stink E. Jones
Stink E. Jones
30 days ago

My long-gone 1991 Camry would like to disagree with the “easiest car to steal” title.

VanGuy
VanGuy
30 days ago

This is irresponsible. You didn’t show us how Kias and Hyundais are being stolen, but now you’re showing us how to steal these!
(/s)

Cheap Bastard
Cheap Bastard
30 days ago

“Before Kia, This Was The Easiest Car In The World To Steal”

Stealing one of these is a come to Jesus moment that should not be ignored!

V10omous
V10omous
30 days ago

But wait, all I hear lately is that the best anti-theft device is a stick shift….

Der Foo
Der Foo
30 days ago
Reply to  V10omous

Stick shift are in a way, unless you are talking about old farts like me. However, old farts like me have generally wised up over the years and don’t go around stealing/jacking cars that much anymore.

A4A
A4A
30 days ago
Reply to  V10omous

That only works in America. In countries where basically everyone knows how to drive stick, so do the thieves.

Andrew Lampart
Andrew Lampart
30 days ago

Vauxhall engineers unknowingly becoming the inventors of push-button start

Musicman27
Musicman27
30 days ago
Reply to  Andrew Lampart

Too bad they didn’t invent touchless entry.

Chronometric
Chronometric
30 days ago

Vauxhall Nova, the analog Hyundai!

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