Older cars are easy to steal and I’m very attached to my old Mercedes, so I fitted a fuel pump cutoff switch which I hid discreetly under the dash.
Fitting a fuel pump cutoff switch for theft prevention is a simple but effective way to disable your car. To fit a cutoff switch you’ll need to:
- Locate Pump Power Supply
- Fit The Kill Switch
- Wire The Switch In Line
- Splice In The Wire
- Fit Heat Shielding
- Solder Connections
- Tape Up Wiring
- Test Kill Switch
Fit A Fuel Pump Kill Switch
Fuel pump type kill switch can only be fitted to a car with an electric fuel pump, if your car is a classic with a mechanical pump, you’ll need to consider fitting a manual fuel valve in the fuel line or an ignition kill switch instead.
To avoid wiring coming loose, which would cause the engine to stall, I’ll like to solder in the wiring. Solder is the best way to join wires, sure you could just twist the wires or use scotch clips, but you run a real risk of them coming loose.
I also use heat-shield sleeves, they protect the wiring from dampness and corrosion.
The first job is to locate the power supply circuit to the fuel pump. Check your fuse box for labeling, or your operator’s manual, the fuses will be numbered.
When you have identified the pump circuit, remove the fuse and cut the wire downstream of the fuse, to be sure your downstream, check the wire for voltage, it should be zero volts with the ignition switch on.
Now find a suitable location for your kill switch, remember you need to be able to reach it from the driver’s seat, but it can’t be too obvious. Use your imagination, your only limitations are accessed.
Places I considered putting my switch are in the glove box, under-seat, in the armrest box, behind the gear selector boot.
Now that you’ve picked your location and fitted the switch. Run two wires from the switch to the cut fuel pump circuit wires. Tidy up your wiring now before cutting them to exact length, often the wiring may need to be routed indirectly.
Strip your wires and fit your heat shielding, twisting the wires before soldering creates a strong connection, push your heat-shielding across the connection and shrink using heat.
Fit your fuse and test your work, the fuel pump will hum momentarily when you power it up. Told you it was simple!
What You’ll Need To Fit The Kill Switch
Avoid unscheduled shopping trips, here’s a shopping list:
- Test Light/DVOM
- Wire Strippers
- Soldering Kit
- Kill Switch
- Black Tape
- Copper Core Wire (apox 6ft)
- Wire Heat-shield
Ignition Kill Switches
Ignition kill switches also known as a dizzy switch are another option, they are a simple switch fitted in the wire from the distributor to the coil. Some cars won’t have a distributor and so the correct wiring may not be obvious. You may need to have a wiring diagram handy.
An ignition kill switch won’t work for more modern vehicles fitted with the CAN network computer-controlled system. This system was used by most manufacturers from the mid-90s onward. We call that a modern classic car.
Anyway, it won’t like extra wiring being added to its looms, this can cause the computer to get confused about what’s going on. It will see the kill switch as a fault and likely fill your computer will a lot of fault codes.
Battery Kill Switches
The battery kill switch is an option for older and younger cars. It’s available as a manual or remote-controlled option, obviously the remote option costing a few extra dollars and a little more work to fit.
The battery kill switch is an effective anti-theft solution, and also prevents your vehicle from short-circuiting and catching fire.
The basic kill switch kills all power and so you’ll need to readjust your dash clock and radio settings every time you use it. More sophisticated kill switches are available that kills power to the starter but allow power to the radio and clock.
Battery kill switches are not suitable for late model cars as they need to be connected to a power supply all the time.
Fuel Line Cut Off Valve
This is a mechanical solution for a mechanical fuel pump. It’s a basic tap that you fit between the gas tank and carburetor. The tap, like the kill switch, is placed somewhere discrete, but inside the car is not advised.
Finding somewhere to hide may take longer than actually fitting it. Fitting it will take no time, simply cut the fuel line, push on the valve and secure it with clamps.
The engine will still start after the tap is turned off, but the engine will soon stall.
How to bypass a kill switch on a car? Bypass the kill switch by removing both connectors from the switch and using a piece of wire to connect both ends together, secure with tape until a more permanent repair is made.
Diy car theft prevention? A great Diy theft prevention quick fix is to remove the fuel pump relay, it will fit easily in your pocket. Another option is to remove your HT coil wire, it too will fit easily in your pocket, your cars going nowhere with gas or spark.
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John Cunningham is an Automotive Technician and writer on Rustyautos.com. He’s been a mechanic for over twenty-five years and has worked for GM, Volvo, Volkswagen, Land Rover, and Jaguar dealerships.
John uses his know-how and experience to write fluff-free articles that help fellow gearheads with all aspects of vehicle ownership, including maintenance, repair, and troubleshooting.