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Discussion Starter · #1 ·
Moved the battery to the trunk and this is my first time wiring a switch with an efi set up. After much reading, I’m a little lost.

It sounds like people were losing tunes in their ecm if the switch was flipped or burning up ecm’s from a voltage spike. I’ve got a 145 amp truck alternator on the car. I’ve also read people using the field wire to the switch instead of the charge wire on the alt.

Which switch should I use and how do I wire this thing correctly so I don’t burn up the alt or computer? Thanks for any help.

I was looking at the flaming river 6 post (fr-1013) that is rated for 150amp continuous and grounds voltage spike as a safety through a resistor to ground.
 

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I have Holley EFI in both of my cars, and have installed and tuned many systems. Holleys ECM main power wires right to the battery, nowhere else! I use 4 pole battery disconnect switches. Main set of terminals kill the positive side of the battery circuit. Small secondary set is used to kill the fuel pump relay. Hit that switch while the engine is running, it will shut off practically instantly. Yes, there is still that #10 wire running to the ECM, but with a 30 amp fuse by the battery, I'm not worried about it.
 

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Discussion Starter · #4 ·
My Holley ECU is directly to the battery terminals , but the keyed 12 volts will shut off with the kill switch .

Hitting the kill switch is no different that turning the key off , Im not sure how that would hurt the ECU .
I’m running a stock computer. But it’s wired to a keyed 12v panel and a constant. Isn’t the switch constant 12? How would wiring the keyed side to the switch work?
 

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Discussion Starter · #5 ·
I have Holley EFI in both of my cars, and have installed and tuned many systems. Holleys ECM main power wires right to the battery, nowhere else! I use 4 pole battery disconnect switches. Main set of terminals kill the positive side of the battery circuit. Small secondary set is used to kill the fuel pump relay. Hit that switch while the engine is running, it will shut off practically instantly. Yes, there is still that #10 wire running to the ECM, but with a 30 amp fuse by the battery, I'm not worried about it.
Does your alt charge wire go to the battery or the switch?
 

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Discussion Starter · #6 ·
I made this panel for my electronics. The fuse panel on the left feeds all my keyed 12v, and the one on the right feeds all my constant 12v needs. The constant 12v panel is fed directly from the battery. Can I just wire it from the battery to the switch, and then to the constant 12v panel? Any spike should blow the fuses correct?


 

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Here is just one article, a transil, discussed here is a type of zener diode. Zeners are used traditionally for voltage regulation, but their "curve" is that at their operating point, the suddenly trigger and then draw LOTS of current, which "clamps" a rising voltage at the trigger point


https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.CD00181783.pdf


https://www.google.com/search?newwi....0i131j0j33i160j33i22i29i30j33i10.-DdqYcdCySc


There is various devices marketed under various names and terminology, marine products for instance, a "load dump" protector.


https://www.electronicdesign.com/po...motive-load-dump-circuit-protection-headaches
 

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Moved the battery to the trunk and this is my first time wiring a switch with an efi set up. After much reading, I’m a little lost.

It sounds like people were losing tunes in their ecm if the switch was flipped or burning up ecm’s from a voltage spike. I’ve got a 145 amp truck alternator on the car. I’ve also read people using the field wire to the switch instead of the charge wire on the alt.

Which switch should I use and how do I wire this thing correctly so I don’t burn up the alt or computer? Thanks for any help.

I was looking at the flaming river 6 post (fr-1013) that is rated for 150amp continuous and grounds voltage spike as a safety through a resistor to ground.


Ecu directly to the battery.

Then do something like mike beck is saying, use the small terminals on the 4 pole switch to kill the fuel pump relay.


With Holley Efi you have to reset the ECU time everytime you kill the main power to the ecu if you want your data log time and dates to match.
 

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Does your alt charge wire go to the battery or the switch?
Alternator goes to the main battery cable running from the switch.

I don't use the switch to shut the engine off, so I have never hurt the diodes in an alternator.

With my main switch off, I only have one live wire in the car, the #10 positive feed to the Holley ECM, which has a 30amp fuse back at the battery. Maybe not 100% NHRA legal, but it has been like this since 1990 and no track has ever aid anything about it. The engine will shut off with the switch.
 

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Discussion Starter · #10 ·
Alternator goes to the main battery cable running from the switch.

I don't use the switch to shut the engine off, so I have never hurt the diodes in an alternator.

With my main switch off, I only have one live wire in the car, the #10 positive feed to the Holley ECM, which has a 30amp fuse back at the battery. Maybe not 100% NHRA legal, but it has been like this since 1990 and no track has ever aid anything about it. The engine will shut off with the switch.
Doesn’t your track test the switch by flipping it off while the car is running? That’s what I’m worried about is burning up an alt when I flip the switch.

Thanks for everyone’s help. Fuel pump relay it is.
 

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You want to run the ECU main positive and negative battery cables directly to the battery. The batter acts as a huge "noise" filter for the ECU.

Some of the early COPOs were having a lot of gremlins because GM didn't run the power cables directly from the Holley ECU to the battery because it was in the back. GM ran them to a power block. A friend of mine had one at Tulsa and couldn't do a burnout with the car when one of the Holley reps came by his pit next to us. The rep said to run the cables directly to the battery and it would resolve the problem. They tried to tell GM this, but they didn't follow this key bit of info. I helped him rewire it and the problem was resolved.
 

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Discussion Starter · #12 ·
You want to run the ECU main positive and negative battery cables directly to the battery. The batter acts as a huge "noise" filter for the ECU.

Some of the early COPOs were having a lot of gremlins because GM didn't run the power cables directly from the Holley ECU to the battery because it was in the back. GM ran them to a power block. A friend of mine had one at Tulsa and couldn't do a burnout with the car when one of the Holley reps came by his pit next to us. The rep said to run the cables directly to the battery and it would resolve the problem. They tried to tell GM this, but they didn't follow this key bit of info. I helped him rewire it and the problem was resolved.
The car ran fine all last year the way I have it wired but if it’s that beneficial I can run the hot to the battery while I’m under the dash splicing into the fuel pump relay.
 

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Doesn’t your track test the switch by flipping it off while the car is running? That’s what I’m worried about is burning up an alt when I flip the switch.

Thanks for everyone’s help. Fuel pump relay it is.
Do they test it every weekend?

I have shut my car off that way a few times a year, simply to show people killing the fuel pump relay on an EFI engine will shut it down FAST! Unlike a carb that has fuel bowls to drain...........

I have never hurt an alternator.

If you run at NHRA tracks, get yourself an Extended Tech so you don't even have to take your car through tech anymore.
 

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Discussion Starter · #14 ·
Do they test it every weekend?

I have shut my car off that way a few times a year, simply to show people killing the fuel pump relay on an EFI engine will shut it down FAST! Unlike a carb that has fuel bowls to drain...........

I have never hurt an alternator.

If you run at NHRA tracks, get yourself an Extended Tech so you don't even have to take your car through tech anymore.
Sweet, thanks Mike. People made it sound like you’ll burn it up doing it once.
 

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If its the stock PCM then wiring the computers 'ignition on' 12V supply through the smaller poles should stop the motor dead, another way to do it.... and if you used the PCM to work the fuel pump relay in the way the LS cars are wired factory, then killing the ignition signal will also kill the fuel pump, as the stock PCM will kill the pump when its not turning over - not getting any rpm signal (crank sensor).
 

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2019 NHRA General Regulations said:
8:4 MASTER CUTOFF
Mandatory when battery is relocated, or as outlined in Class Requirements. An electrical power cutoff switch (one only) must be installed on the rearmost part of each vehicle and be easily accessible from outside the car body. This cutoff switch must be connected to the positive side of the electrical system and must stop all electrical functions including magneto ignition. The off position must be clearly indicated with the word “OFF.” If switch is “push/pull” type, “push” must be the action for shutting off the electrical system, “pull” to turn it on. Any rods or cables used to activate the switch must be minimum 1/8-inch diameter. Plastic or keyed switches prohibited. Switches and/or controls must be located behind rear wheels on rear-engine dragsters.
The purpose of the master cutoff switch is not just to kill the engine, but to shut down the whole electrical system. That way, in the event of a crash, the safety guys can hit the kill switch and no wires will be hot except between the battery and the switch. I doubt tech would mind if you direct-wired the ECU so you don't fry it or lose your tune, but everything else should be dead when the master cutoff switch is in the off position.
 

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The purpose of the master cutoff switch is not just to kill the engine, but to shut down the whole electrical system. That way, in the event of a crash, the safety guys can hit the kill switch and no wires will be hot except between the battery and the switch. I doubt tech would mind if you direct-wired the ECU so you don't fry it or lose your tune, but everything else should be dead when the master cutoff switch is in the off position.
It says "must stop all electrical functions", not "kill all power". An alternator charging wire, ECU power feed, and/or MSD power feed wired directly to the battery are non functioning, and therefore legal.
 

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Discussion Starter · #18 ·
If its the stock PCM then wiring the computers 'ignition on' 12V supply through the smaller poles should stop the motor dead, another way to do it.... and if you used the PCM to work the fuel pump relay in the way the LS cars are wired factory, then killing the ignition signal will also kill the fuel pump, as the stock PCM will kill the pump when its not turning over - not getting any rpm signal (crank sensor).
I’m wiring the computer directly to the battery so the switch won’t turn it off. I don’t wanna deal with a throttle relearn, which is apparently what happens.
 

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The purpose of the master cutoff switch is not just to kill the engine, but to shut down the whole electrical system. That way, in the event of a crash, the safety guys can hit the kill switch and no wires will be hot except between the battery and the switch. I doubt tech would mind if you direct-wired the ECU so you don't fry it or lose your tune, but everything else should be dead when the master cutoff switch is in the off position.
Tech won't have a problem with it because many Stock Eliminator cars run a battery in the back and are required to have an equal battery in the front of the same size. There is a huge hot positive cable running from the battery in the front to the switch at the back in all the cars even if not fuel injected that have this set up.
 
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