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PostPosted: March 19, 2020, 1:48 pm 
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Joined: December 4, 2010, 1:53 pm
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Location: Edmonton, Alberta, Canada
Having had the unpleasant experience of being hit from behind in my Miata a few years ago, I looked into getting a switch that shuts off the fuel pump in the event of an accident. I couldn't find anything about it here, but I found lots of info from hot rodders. Seems a lot of them use a common Ford "inertia switch". The photo below is one taken from a 93 Crown Victoria. I used one from a 2004 Lincoln Towne Car which looks identical, and it did not have the heavy bracket around it. Look in the left rear trunk. Apparently they can be found in a Taurus as well. Make sure to install with the red reset button facing up. This switch is supposed to work in the event of a front or rear collision, or from a rollover.
cheers
Doug


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PostPosted: March 19, 2020, 2:05 pm 
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Joined: July 17, 2008, 9:11 am
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Location: West Chicago,IL
Having been rear ended many times in my DD's, frankly, one of the least of my worries about being rear ended in a Locost is shutting down the fuel pump. :ack: Other areas of impact, good idea. Don't forget a rollover check valve in the fuel vent line. I used one from a Jeep of some vintage/model.

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PostPosted: March 19, 2020, 2:25 pm 
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Joined: December 22, 2006, 2:05 pm
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It has been brought up many times. Try searching for "inertia". I've been promoting them since about 2008.
Most fords have them from 87-up.
Everything I build has one.
Cheap insurance. :cheers:

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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PostPosted: March 20, 2020, 12:04 pm 
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Joined: December 4, 2011, 6:19 pm
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Does anyone have any details on the performance of these Ford switches? How many G's required to activate? Reliability, as in what percentage of the time do they trip if exposed to the correct G load? Is the red button a reset? If so, how many times can one of these switches activate before requiring replacement?

The Emergency Location Transmitter (ELT) in small airplanes is fired by a G switch but they are notoriously known for failure with some people reporting failure rates in the G switch as high as 38% in real world situations. And, that's despite a regulation that the switches must be inspected each year by an approved avionics repair technician.

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PostPosted: March 20, 2020, 1:58 pm 
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It is a plated steel ball in a magnetic cup that bridges the ground side of a relay. It should be mounted in a clean dry place out of direct sunlight. The button re-seats the ball if it rolls out of the cup. That is why the orientation is important.

You could remove the screws and bump it with your hand to simulate an impact that should unseat the ball.

Some info on the ELT inertia switch testing: https://ntrs.nasa.gov/archive/nasa/casi ... 010544.pdf

Mazda used an output from the VAF to keep the pump on, so if the engine died, the spring loaded vane returns to its stop, and the pump stops.
GM has used oil pressure so if the engine stops, the pump stops.
I expect newer vehicles will stop the pump based on no trigger input from the engine.

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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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PostPosted: March 20, 2020, 2:06 pm 
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Joined: April 23, 2006, 8:26 pm
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Location: SoCal
I got mine from a Ford Mustang. Pretty sure it's the same switch in all their cars. The switch is just a ball sitting in a depression at the top of a cone. Enough sideways force in any direction knocks it off its perch and shuts off the pump.

Oh, and wire it so that it's in series with the fuel pump relay coil, so that you aren't running full fuel pump current through it.

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PostPosted: March 20, 2020, 2:20 pm 
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Joined: December 22, 2006, 2:05 pm
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Inside a couple different types for ford.


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Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12


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PostPosted: April 14, 2020, 12:50 pm 
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Joined: March 30, 2011, 7:18 am
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Location: central Arkansas
> how many G's

By the unscientific method of slapping mine against my hand, "a lot". Mine never triggered at the track, so I didn't pursue it further.

I mounted mine by the shifter boot, within easy reach if I needed to reset it. The EFI system I had would continue to run as long as there was fuel in the surge tank if someone didn't turn the key or disconnect switch, even upside-down.


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