1 (edited by ebutka 2022-04-29 06:46 PM)

Topic: Electrical Cut Off Questions - Location and Wiring

While I’m waiting on the cage to be built, I’m trying to figure out the proper location and wiring for kill switch. We were thinking of putting it next to the seat, at the green circle. Easy for the driver to access and easy for someone outside to reach it. That would be fine, right?

As for wiring it, at first it seemed like we could put it in between the positive line on the battery. After lots reading, it seems like we’d also need to run a line from the alternator. Originally we bought a 2 pole switch, but now need a 4 pole? Slightly confused on how to properly wire the kill switch without hurting components. Anything helps, thanks!

https://imgur.com/a/OhMZMTg

2 (edited by DirtyDuc 2022-04-29 07:08 PM)

Re: Electrical Cut Off Questions - Location and Wiring

If you put it there, you likely won't be able to see it when strapped in.

There are ways to make a two pole work with a modern car. I don't know them, I just know there are ways.

That guy

3 (edited by Guildenstern 2022-04-29 07:19 PM)

Re: Electrical Cut Off Questions - Location and Wiring

You want it in eyeline not down there.

You want a 6 Pole with a discharge resistor for anything with electronic fuel mixture of any sort.
https://cdn.shopify.com/s/files/1/0190/0573/4978/products/ogracing-killswitch-installation_400x.jpg?v=1618515467

https://www.ogracing.com/products/batte … killswitch

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Re: Electrical Cut Off Questions - Location and Wiring

Search through the forum, you will find that this topic has been discussed many, many times.

For example: https://forums.24hoursoflemons.com/view … p?id=39587

When you pull the kill switch, you want it to do the following:

- stop the engine from running (the only thing that the tech inspector will actually check - they don't ask you how its wired)

To add additional safety margin, it would also be good to have it do these things too:

- disconnect the alternator so that it can't keep the engine running
- stop the fuel pump from pumping (assuming an electrical fuel pump)
- remove the battery voltage from as much of the car's wiring as possible (especially around sources of fuel)
- reduce the likelyhood of alternator damage from 'load dump' by connecting a power resistor across its output when you disconnect it

Our switch is located in the center of the car near the gear lever, that was a requirement for Chump Car (at least it was back in 2014 when we did a few of those). We added a remote cable pull just inside the drivers door, on the roll cage front downtube so it could be actuated at either location. Never had an issue with a Lemons tech inspector in the last 8 years.

We Audi Be Faster
'85 Audi Coupe G(in &) T(onic)

Re: Electrical Cut Off Questions - Location and Wiring

In our Lemons approved car, we have the switch mounted about there, but there are two additional pulls.  One at base of windshield outside in cowl area on passenger side and one at dashboard just inside driver window.  I always like to have electrical and fire pulls on both sides of the car.  Never know side is against the wall or otherwise not accessible.

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Re: Electrical Cut Off Questions - Location and Wiring

I like to install the switch on the A pillar downbar somewhere within easy reach from both inside and outside.  As to the wiring, I'm sure people will post all kinds of confusing diagrams and explanations of how this that and the other of how it should be.  Press the Easy Button.    Battery and alternator output on the samevpole on one side and everything else you need to power the car on the other pole.  Every car I've had has worked just fine like that without hurting anything and that's exactly how the head of Lemons tech wires his.

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Gone bye-bye
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7 (edited by -SDR- 2022-05-01 08:02 PM)

Re: Electrical Cut Off Questions - Location and Wiring

cheseroo wrote:

I like to install the switch on the A pillar downbar somewhere within easy reach from both inside and outside.  As to the wiring, I'm sure people will post all kinds of confusing diagrams and explanations of how this that and the other of how it should be.  Press the Easy Button.    Battery and alternator output on the samevpole on one side and everything else you need to power the car on the other pole.  Every car I've had has worked just fine like that without hurting anything and that's exactly how the head of Lemons tech wires his.

What he said.....

We have a two pole.  One pole is connected to both the battery and alt power output. Yes, power to the alt output all the time, but not the field coil wire.  Everything else is on the other pole.  The only issue you will have with this set up is if you have an electric fan, but easily fixed with a big diode.

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Re: Electrical Cut Off Questions - Location and Wiring

We have two kill switches, one setup for the driver, one for outside access. This is overkill, but we did it anyway. Positive lead off the battery goes directly to the exterior mounted 2 pole switch. From there it goes to the interior A-pillar mounted 6 pole switch. Then that feeds the rest of the car. the 6 pole takes care of cutting the car cleanly and protecting things like the alternator, this is the switch we use at tech. The 2 pole may not protect things, but in an emergency I really don't care. I'd rather potentially nuke an alternator if it gets a driver out safe. It made me feel better to have two exterior accessible switches rather than just one.



The easiest way to wire the 6 poles is to find the main 12V feed to the ignition switch and cut it, then route it to the appropriate terminals on the kill switch. In operation this means you're basically just turning off the ignition switch in parallel with cutting the battery. This should mostly cleanly turn off fuel pumps, ecus, etc. Wire up the alternator dump resistor and you should be good to go.


Or wire up a 2 pole as described above, basically the same thing with a different switch.

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9 (edited by duthehustle93 2022-05-02 10:29 AM)

Re: Electrical Cut Off Questions - Location and Wiring

cheseroo wrote:

I like to install the switch on the A pillar downbar somewhere within easy reach from both inside and outside.  As to the wiring, I'm sure people will post all kinds of confusing diagrams and explanations of how this that and the other of how it should be.  Press the Easy Button.    Battery and alternator output on the samevpole on one side and everything else you need to power the car on the other pole.  Every car I've had has worked just fine like that without hurting anything and that's exactly how the head of Lemons tech wires his.

+1 ... drivers side A pillar down bar kills two birds with one stone. Allows crew and driver to kill it and it's very visible.

On both cars I run a 4 pole... big ones on battery positive, and small ones interrupt a circuit that will make the engine shut off. Miatas have an "engine" fuse that controls spark and fuel and I prefer to interrupt that circuit.. easy and works great. On the pinata miata the previous owners who wired it interrupted the ignition switch (the thing you stick the key in) to mimic removing the key... works fine for us.

Full Ass Racing
#455 Piñata Miata - 1990 Miata
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Re: Electrical Cut Off Questions - Location and Wiring

Another vote for A-pillar

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Re: Electrical Cut Off Questions - Location and Wiring

RSB wrote:

When you pull the kill switch, you want it to do the following:

- stop the engine from running (the only thing that the tech inspector will actually check - they don't ask you how its wired)

Even though the typical test at tech inspection just verifies that the engine stops running, please, everyone, follow Rule 3.7.1 which states that "all electricity... must be interrupted by the kill switch." It's not that hard to wire it properly to kill all circuits and it's very much not a good thing to have unnecessary electrical surprises for the driver and emergency crew during an incident. If that's not enough incentive to do it right, keep in mind that if an official notices live circuits during, say, fueling (lights during a 24-hour race are a particularly obvious example), you will find your potential track time being consumed in an awkward conversation about why kill switches need to kill everything and may very well even be told to fix it before returning to track, especially if something like the fuel pump can keep running when the kill switch is off. If you need to flip more than just the kill switch to turn off every circuit in the car, then it is not wired correctly.

1982 MG Metro 1300: IOE 2015 Pacific Northworst GP, Longest Distance 2010 Cd'L Box Wine Country Classic
1980 KV Mini 1: Worst of Show and Fright Pig Supremo 2009 Concours d'Lemons
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