NHRA legal kill switch - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 19 Old 07-07-2017, 01:09 PM Thread Starter
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NHRA legal kill switch

I know the forums are littered with threads on the correct way to run an nhra legal kill switch. I understand it has to kill all electrical functions of the car, has to be on the positive side of the system, and the push pull, on off thing. What I don't understand is how to kill the alternator to kill the engine. This is on a carbed setup. Is it the same way as doing it on EFI. I think I've been reading up too much and confusing myself.


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post #2 of 19 Old 07-07-2017, 07:27 PM
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It has to kill battery and alternator, there should be no difference in efi vs carb. Effectively it will shut car off when pulled.

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post #3 of 19 Old 07-07-2017, 08:28 PM
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To clarify, it interrupts the alternator, I personally ran 2 wires, the alternator to battery, and alternator to main, therefore cutting the battery off and the alternator at the same time.
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post #4 of 19 Old 07-07-2017, 09:28 PM Thread Starter
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I understand that too, just can't visualize it without cutting the factory alternator harness and running wires to and from the trunk of the car. I'm somewhat intimidated by automotive electrical systems.

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post #5 of 19 Old 07-07-2017, 09:40 PM Thread Starter
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I'm planning on using the factory alternator and wiring harness, not a 3G alternator, if that matters.

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post #6 of 19 Old 07-07-2017, 09:51 PM
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Do a search. There's a ton of threads about the subject. There has been lot of discussion about how the NHRA legal method leaves a hot wire that could potentially short. I believe guys have mentioned how to make it legal and eliminate that hot wire.

'87, 105,000 mile stk short, SN89 Paxton 5 LBS, X303 Hds, E303, Cobra Int, 70 mm TB, 30# injrs, 1 5/8 full leng, no cats, 2 1/2 w/dumps, A5, 3.73, ET R's, Frnt Drag Eibach sprngs, Baseline Relocated upprs, HPM lwr arms, stk rear sprngs 1 coil cut, adj. struts shocks, 3150 w/dr. 1.60 11.39 118.
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post #7 of 19 Old 07-07-2017, 10:01 PM
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And definitely make it fused link. Cheap insurance. I understand how confusing it seems, I had to draw it out, and even then, I had questioned myself. I had mine as a "battery cutoff" until I realized, just like testing an alternator, with the car running; it wouldn't kill the car because the alternator was running it. From there I basically wired the alternator through the same cutoff as well as to kill all power.
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post #8 of 19 Old 07-07-2017, 10:27 PM Thread Starter
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I've searched and read till none of it makes sense. I just volunteered my brother in law who is a John Deere electrical engineer to help me with it. The way he drew it out made it seem simple. The only real difference between the tractor cut off switch and the way mine will be is John Deere kills the ground not the positive side.

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post #9 of 19 Old 07-08-2017, 07:26 AM
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Originally Posted by boostup89 View Post
I've searched and read till none of it makes sense. I just volunteered my brother in law who is a John Deere electrical engineer to help me with it. The way he drew it out made it seem simple. The only real difference between the tractor cut off switch and the way mine will be is John Deere kills the ground not the positive side.
The ground side is not legal because in a wreck, something else (damaged parts) could provide a ground. I don't have time now, but there's a diagram on here somewhere.

'87, 105,000 mile stk short, SN89 Paxton 5 LBS, X303 Hds, E303, Cobra Int, 70 mm TB, 30# injrs, 1 5/8 full leng, no cats, 2 1/2 w/dumps, A5, 3.73, ET R's, Frnt Drag Eibach sprngs, Baseline Relocated upprs, HPM lwr arms, stk rear sprngs 1 coil cut, adj. struts shocks, 3150 w/dr. 1.60 11.39 118.
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post #10 of 19 Old 07-08-2017, 07:56 AM Thread Starter
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So which wires from the alternator need to be spliced and ran to the cut off switch? If memory serves me correctly, my alternator has two plugs with 3 terminals.


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post #11 of 19 Old 07-09-2017, 09:29 PM
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This should get you started, I found it with a search. ;-) ;-) ;-)
https://forums.corral.net/forums/drag...-once-all.html

'87, 105,000 mile stk short, SN89 Paxton 5 LBS, X303 Hds, E303, Cobra Int, 70 mm TB, 30# injrs, 1 5/8 full leng, no cats, 2 1/2 w/dumps, A5, 3.73, ET R's, Frnt Drag Eibach sprngs, Baseline Relocated upprs, HPM lwr arms, stk rear sprngs 1 coil cut, adj. struts shocks, 3150 w/dr. 1.60 11.39 118.
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post #12 of 19 Old 06-30-2018, 09:55 AM Thread Starter
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Just getting around to wiring this switch. My switch has two 7/16" terminals, one from the battery positive, the other to start solenoid. Then it has two 1/4" might be 5/16" terminals, one from alternator, the other to battery positive. Is it normal for the alternator terminals on a Killswitch to be so much smaller than the other terminals?

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post #13 of 19 Old 06-30-2018, 11:55 AM
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The wire to the alternator is smaller as you are just cutting the alternator field connection and not the charging wire. I used a 12 AWG wire from the smaller post to the alternator when I wired mine in.
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post #14 of 19 Old 06-30-2018, 12:35 PM Thread Starter
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So what wire from the alternator/harness needs ran to the smaller post?

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post #15 of 19 Old 06-30-2018, 08:06 PM Thread Starter
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Forgot to mention, I'm using the stock non 3G alternator. Also on my Killswitch, in the on position, should either of the two smaller terminals be hot?

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post #16 of 19 Old 06-30-2018, 11:48 PM
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Cole Hersee 79503. DPST main disconnect. Batt goes on the two B terminals, then the alt goes on the two "F" terminals (field). It is specifically designed for this purpose and works exactly as designed when wired properly. As a friendly reminder, it's best to test the switch before every race day to make sure it works.


http://www.littelfuse.com/~/media/co...-2d-prints.pdf

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post #17 of 19 Old 07-01-2018, 08:13 AM Thread Starter
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Thanks, that is the exact switch I have in place. I got it figured out now.

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post #18 of 19 Old 07-11-2018, 05:19 PM
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Quote:
Originally Posted by toddturbo View Post
Cole Hersee 79503. DPST main disconnect. Batt goes on the two B terminals, then the alt goes on the two "F" terminals (field). It is specifically designed for this purpose and works exactly as designed when wired properly. As a friendly reminder, it's best to test the switch before every race day to make sure it works.


http://www.littelfuse.com/~/media/co...-2d-prints.pdf
You mean 75903? Those two "F" terminals are only rated for what, 20 amps max? How can those handle your typical alternator which puts out way more amps? I think the correct switch needed is going to be a Longacre Racing 45782 which can handle the amp load.

This way of wiring leaves you with a hot alt wire. This is how I just wired mine because I trusted what the NHRA says. When I hit my cut off switch, this is going to leave a hot wire going to the alt. No thanks.



This new diagram below that uses an actual 2 pole cutoff switch (Longacre Racing 45782) that can handle the high amp load cuts off power to everything and also this wiring diagram (optional) ensures that your starter wire is not hot when the car is not being started. It's called Painless Performance Products 30203 remote start solenoid. Why install a painless performance relay 50105 when all I have to do is change out the kill switch? I may or may not install the 30203 remote start solenoid. Anyone using one of these remote start solenoids?

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post #19 of 19 Old 09-11-2018, 12:41 AM
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I was reading the other thread that SpeedThrills posted and I'm still a bit confused.
Would this be an NHRA legal way of wiring a kill switch using a Flaming River FR1003-2 Cut-Off Switch?
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