Topic: Kill switch wiring, do I need to wire separate ignition cutoff?

I did search the forums for an answer to this question and I did not find anything. My apologies if I've missed it.

I bought the kill switch from the Lemons store, this one: http://store.24hoursoflemons.com/produc … switch.htm

The wiring diagram image is below for reference. This diagram and the many threads on the forum make it very clear and easy to understand how to wire this up correctly.

On a modern ECU driven electronic fuel injection, coil on plug car, is it necessary to wire in the ignition switch/coil cutoff? On a modern ECU driven electronic fuel injection car, I believe that cutting off the battery and grounding out the alternator current (the "W or 1" connection) will very rapidly cut off power to the fuel pump, ECU, injectors, coils, etc.

For a non-ECU carbureted car with a mechanical fuel pump, I can see the extra value of adding the ignition coil cutoff, but I don't think that wiring up the ignition/coil cutoff adds any extra protection for a modern car.

So, my questions are:

1. Will my car pass tech if I don't wire in the ignition switch cutoff depicted in the diagram below (the "Z or 2" connection)?

2. Separate from the question of passing tech, on a modern ECU driven electronic fuel injection car, does wiring in the ignition switch cutoff provide any extra protection?


https://c1.staticflickr.com/1/722/32923352235_5f6f479b30_b.jpg

Re: Kill switch wiring, do I need to wire separate ignition cutoff?

I've always had mine (GM EFI w/distributor) wired up to just kill the battery power to everything and the alternator source wire.  Once the ECU loses power, its not running anymore.  That's what they're looking for, the car to shut off when the switch is disengaged.

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Re: Kill switch wiring, do I need to wire separate ignition cutoff?

To answer my own question, I did indeed need to wire up the "Z or 2" connection to kill the engine. Without that wired up, the engine did not die when I threw the kill switch, the alternator continued to provide power.

To determine which circuit to wire into "Z or 2", I started the engine and then pulled fuses one at a time until I found one that killed the engine when I pulled it, it was the fuel injection power circuit. I then found the correct wire that led out of that fuse and wired it into the kill switch. Works perfect now.

Re: Kill switch wiring, do I need to wire separate ignition cutoff?

Is a fuel pump kill switch sufficient or does it need to be full electrical system?

Re: Kill switch wiring, do I need to wire separate ignition cutoff?

psycho_driver wrote:

Is a fuel pump kill switch sufficient or does it need to be full electrical system?

The switch must interrupt the entire electrical system. The point is not just to stop the engine but to minimize the potential for electrical and/or combustion hazards during and after an incident. With the switch off the car should be as inert as possible.

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Re: Kill switch wiring, do I need to wire separate ignition cutoff?

psycho_driver wrote:

Is a fuel pump kill switch sufficient or does it need to be full electrical system?

Take a look at the image in the first post in this thread. The battery positive goes through the kill switch first, before going anywhere else so that, if the car is already not running, and the kill switch is thrown, the car will have no power, meaning not only that it cannot start, but also that no circuits have power. A fuel pump kill switch will not be sufficient for this part of the requirement.

HOWEVER, the kill switch must also kill the engine when it is running, and that is a different matter. On most cars, you will find that if the car is running, just disconnecting the battery will not stop the engine. So you need to also wire up the "Z or 2" terminals on the kill switch (again, see the diagram in the first post) to something that will stop the engine from running when it is opened. Running the fuel pump power through the "Z or 2" terminals on the kill switch will kill the engine, but, depending on the car, the engine may continue to run for some time after killing the fuel pump power and may or may not pass tech (I don't know). For my car, I pulled random fuses with the car running to find one that killed the car immediately when pulled, and then I tracked down the wire for that fuse behind the fuse box and wired that into the "Z or 2" terminal on the kill switch.

Re: Kill switch wiring, do I need to wire separate ignition cutoff?

To those that run the VW Audi  or a bosh alt you must wire it up like the pic above or you will kill the alt over time if you use the master switch to kill it on stops. When you kill it it will spike the alt with out that resister in the ground. You know I know DRVOLKS here !!

Re: Kill switch wiring, do I need to wire separate ignition cutoff?

I can tell you that simply cutting the fuel pump will not be enough. There is enough residual pressure in the fuel lines for the engine to run for a short time after cutting. Tech is looking for the engine to die immediately when the switch is flipped, if there is a lag, you fail.

The point of the kill switch rule is that in an emergency you need to do two things. 1) stop the engine. 2) remove power completely from the car. You want to make sure that in an emergency you have removed all sources of potential escalation. You don't want a fuel pump continuing to push gas through a burst line and making a fire worse. You don't want live wires if something got cut and crew needs to reach into the car, or sparks creating an ignition source. Simply stopping the engine is not the main goal, the goal is removal of all power to everything in the car.


As mentioned cars will run off the alternator if the battery is removed from the circuit. So the easiest way we've always found to accomplish the goals of stopping the engine and removing power is find the wire that feeds main power into the ignition switch, run that through Z/2 on the diagram above. Then run the main battery cable through the main posts of the switch before it branches to anything in the car. That way when you flip the kill switch you have essentially turned the key off which will stop the engine and all accessories, and then once the alternator is spun down the battery is isolated and there are no power sources to the car.


The alternator drain resistor is important too if you wish to not kill the alternator as DRVOLKS mentioned. In a normal setup the alternator will dump any power it's creating during shutdown into the battery. If you remove the battery it needs somewhere to go. Those large power resistors give it something to dump through and dissipate.

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Re: Kill switch wiring, do I need to wire separate ignition cutoff?

TheEngineer wrote:

. You don't want a fuel pump continuing to push gas through a burst line and making a fire worse.

+MANY

In the case of the fire on the SHO the fans and fuel pump
were running at full speed leading to some serious flameage.
Had the driver used the kill switch, not only would the fuel pump
have shut down, but the fans would have stopped pumping hundreds
of CFM of air to feed the fire.
You want all sources of power disconnected from the electrical system.

I've killed a few Bosch voltage regulators figuring out that the alternator
was continuing to generate electricity and needed a place to dump it.

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10

Re: Kill switch wiring, do I need to wire separate ignition cutoff?

OMG

I think y'all just clued me into why our brand new alternator died so fast.  Never had a problem leaving off the grounding side of the starter wire  in the kill switch before our recent engine swap but now I'll bet the new setup not being able to get rid of the leftover power killed the alternator. 

I just installed a new alternator and will fix the kill switch wiring tonight.  Just in time for the race in two weeks!

Thanks for the info that was already out there but I wasn't paying attention to!

Re: Kill switch wiring, do I need to wire separate ignition cutoff?

DelinquentRacer wrote:

+MANY

In the case of the fire on the SHO the fans and fuel pump
were running at full speed leading to some serious flameage.
Had the driver used the kill switch, not only would the fuel pump
have shut down, but the fans would have stopped pumping hundreds
of CFM of air to feed the fire.
You want all sources of power disconnected from the electrical system.

I've killed a few Bosch voltage regulators figuring out that the alternator
was continuing to generate electricity and needed a place to dump it.

FIRE BAD

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